System and method for measuring the head position and postural sway of a subject

ABSTRACT

A system and method for measuring the head position and postural sway of a subject is disclosed herein. The system generally includes a head position detection device, a postural sway detection device, and a data processing device operatively coupled to the head position detection device and the postural sway detection device. During the execution of the method, the position of the head of the subject is measured using the head position detection device, and the postural sway of the subject is measured using the postural sway detection device. Also, during the execution of the method, it is determined whether the subject is displacing his or her head over a prescribed range by comparing the head position information determined by using the head position measurement device to a predetermined head displacement range.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. Nonprovisional patent applicationSer. No. 15/809,705, entitled “System And Method For Measuring EyeMovement And/Or Eye Position And Postural Sway Of A Subject”, filed onNov. 10, 2017, which is a continuation-in-part of U.S. Nonprovisionalpatent application Ser. No. 14/689,632, entitled “System And Method ForMeasuring Eye Movement And/Or Eye Position And Postural Sway Of ASubject”, filed on Apr. 17, 2015, now U.S. Pat. No. 9,814,430; thedisclosure of each of which is hereby incorporated by reference as ifset forth in their entirety herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable.

INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISK

Not Applicable.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention generally relates to the combined measurement of headposition and postural sway of a subject or patient. More particularly,the invention relates to a system and method for measuring head positionand postural sway of a subject.

2. Background

Patients with damage to the inner ear balance system suffer from lack ofhead-eye coordination. That means, when these patients move the head,their vision becomes blurry and their balance function deterioratesaccordingly. As one example of a cause, damage to the inner ear balancesystem may occur as a result of the patient sustaining a traumatic braininjury (TBI) or concussion.

These patients with damaged inner ear balance systems are often givenhead-eye coordination exercises to regain function. However, with theconventional rehabilitation methods currently used, there is no way toquantify the head, eye, and postural movements during such exercises inorder to determine if the patients are regaining the normalfunctionality of their inner ear balance systems.

What is needed, therefore, is a system and method for measuring eyemovement/eye position, head position, and/or postural sway of a subjectthat provides quantification of head, eye, and postural movements duringhead-eye coordination exercises. Moreover, a system and method formeasuring eye movement/eye position, head position, and/or postural swayof a subject or patient is needed that enables a patient's functionalstatus to be objectively documented before, during, after therapy.Furthermore, a need exists for a system and method for measuring eyemovement/eye position, head position, and/or postural sway of a subjector patient that enables a medical condition to be assessed (e.g., atraumatic brain injury (TBI) or concussion) so that the proper treatmentprocedures can be implemented.

BRIEF SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a system and methodfor measuring head position and postural sway of a subject thatsubstantially obviates one or more problems resulting from thelimitations and deficiencies of the related art.

In accordance with one aspect of the present invention, there isprovided a method for concurrently measuring the head position andpostural sway of a subject. The method includes the steps of: (i)providing a head position measurement device configured to measure aposition of a head of the subject while the subject performs a balancetest and/or a concussion screening test; (ii) providing a postural swaydetection device, the postural sway detection device configured todetect a postural sway of the subject while the subject performs thebalance test and/or the concussion screening test, the postural swaydetection device being configured to output one or more signals that arerepresentative of the detected postural sway of the subject; (iii)providing a data processing device operatively coupled to the posturalsway detection device, the data processing device configured to receivethe one or more signals that are representative of the detected posturalsway of the subject, the data processing device further configured todetermine the postural sway of the subject using the one or moresignals; (iv) positioning the subject in an upright position on asurface; (v) instructing the subject to displace his or her head backand forth in an oscillatory manner over a prescribed range; (vi)measuring the position of the head of the subject using the headposition measurement device; (vii) measuring the postural sway of thesubject using the postural sway detection device while measuring theposition of the head of the subject, and outputting the one or moresignals that are representative of the postural sway of the subject fromthe postural sway detection device; (viii) determining, by using thehead position measurement device, head position information for thesubject; (ix) determining, by using the data processing device, posturalsway data for the subject from the one or more signals output by thepostural sway detection device; and (x) determining whether the subjectis displacing his or her head over the prescribed range by comparing thehead position information determined by using the head positionmeasurement device to a predetermined head displacement range.

In a further embodiment of this aspect of the present invention, thehead position measurement device comprises at least one of thefollowing: (a) one or more inertial measurement units, (b) a videocamera, (c) an infrared sensor, (d) an ultrasonic sensor, (e) a lightsource configured to project a light beam onto a surface, and (f) amarkerless motion capture device; and the step of measuring the headposition of the subject further comprises measuring the head position ofthe subject using at least one of: (a) the one or more inertialmeasurement units, (b) the video camera, (c) the infrared sensor, (d)the ultrasonic sensor, (e) the light source projecting the light beamonto the surface, and (f) the markerless motion capture device.

In yet a further embodiment, the postural sway detection devicecomprises at least one of the following: (a) a force or balance plate,(b) one or more inertial measurement units, (c) an optical motioncapture device, (d) an infrared motion capture device, and (e) amarkerless motion capture device; and the step of measuring the posturalsway of the subject using the postural sway detection device furthercomprises measuring the postural sway of the subject using at least oneof: (a) the force or balance plate, (b) the one or more inertialmeasurement units, (c) the optical motion capture device, (d) theinfrared motion capture device, and (e) the markerless motion capturedevice.

In still a further embodiment, the head position measurement device isoperatively coupled to the data processing device, and the dataprocessing device is further configured to receive one or more headposition signals that are representative of the detected position of thehead of the subject from the head position measurement device, and todetermine the head position information for the subject from the one ormore head position signals output by the head position measurementdevice.

In yet a further embodiment, the step of instructing the subject todisplace his or her head back and forth over the prescribed rangefurther comprises instructing the subject to displace his or her headback and forth in the oscillatory manner over a prescribed angularrange; and the step of determining head position information for thesubject further comprises determining, by using the data processingdevice, an angular position of the head of the subject as the subjectdisplaces his or her head over the prescribed angular range.

In still a further embodiment, the head position measurement devicecomprises one or more inertial measurement units, the one or moreinertial measurement units including an accelerometer configured todetect linear acceleration and a gyroscope configured to detect angularvelocity; and the step of measuring the position of the head of thesubject using the head position measurement device further comprisesmeasuring the position of the head of the subject using theaccelerometer and the gyroscope of the one or more inertial measurementunits, and the position of the head of the subject is determined by thedata processing device based upon the linear acceleration detected bythe accelerometer and the angular velocity detected by the gyroscope.

In yet a further embodiment, the postural sway detection devicecomprises a force or balance plate, the force or balance plate includesa force receiving component having a top surface for receiving at leastone portion of the body of the subject; and at least one forcetransducer disposed underneath the force receiving component, and the atleast one force transducer supporting the force receiving component, theat least one force transducer configured to sense one or more measuredquantities and output the one or more second signals, the one or moresecond signals being representative of forces and/or moments beingapplied to the top surface of the force receiving component of the forcemeasurement assembly by the subject, and the at least one forcetransducer comprising a pylon-type force transducer or a forcetransducer beam.

In still a further embodiment, the head position measurement devicecomprises a light source configured to project a light beam onto asurface.

In accordance with another aspect of the present invention, there isprovided a method for concurrently measuring the head position andpostural sway of a subject. The method includes the steps of: (i)providing a head position measurement device configured to measure aposition of a head of the subject while the subject performs a balancetest and/or a concussion screening test, the head position measurementdevice comprising at least one of the following: (a) one or moreinertial measurement units, (b) a video camera, (c) an infrared sensor,(d) an ultrasonic sensor, (e) a light source configured to project alight beam onto a surface, and (f) a markerless motion capture device;(ii) providing a postural sway detection device, the postural swaydetection device configured to detect a postural sway of the subjectwhile the subject performs the balance test and/or the concussionscreening test, the postural sway detection device being configured tooutput one or more signals that are representative of the detectedpostural sway of the subject; (iii) providing a data processing deviceoperatively coupled to the postural sway detection device, the dataprocessing device configured to receive the one or more signals that arerepresentative of the detected postural sway of the subject, the dataprocessing device further configured to determine the postural sway ofthe subject using the one or more signals; (iv) positioning the subjectin an upright position on a surface; (v) instructing the subject todisplace his or her head back and forth in an oscillatory manner over aprescribed angular range; (vi) measuring the position of the head of thesubject using the head position measurement device that comprises atleast one of: (a) the one or more inertial measurement units, (b) thevideo camera, (c) the infrared sensor, (d) the ultrasonic sensor, (e)the light source projecting the light beam onto the surface, and (f) themarkerless motion capture device; (vii) measuring the postural sway ofthe subject using the postural sway detection device while measuring theposition of the head of the subject, and outputting the one or moresignals that are representative of the postural sway of the subject fromthe postural sway detection device; (viii) determining, by using thehead position measurement device, an angular position of the head of thesubject as the subject displaces his or her head over the prescribedangular range; (ix) determining, by using the data processing device,postural sway data for the subject from the one or more signals outputby the postural sway detection device; and (x) determining whether thesubject is displacing his or her head over the prescribed angular rangeby comparing the angular position of the head of the subject determinedby using the head position measurement device to a predetermined headdisplacement range.

In a further embodiment of this aspect of the present invention, thehead position measurement device comprises a light source configured toproject a light beam onto a surface.

In yet a further embodiment, the postural sway detection devicecomprises at least one of the following: (a) a force or balance plate,(b) one or more inertial measurement units, (c) an optical motioncapture device, (d) an infrared motion capture device, and (e) amarkerless motion capture device; and the step of measuring the posturalsway of the subject using the postural sway detection device furthercomprises measuring the postural sway of the subject using at least oneof: (a) the force or balance plate, (b) the one or more inertialmeasurement units, (c) the optical motion capture device, (d) theinfrared motion capture device, and (e) the markerless motion capturedevice.

In still a further embodiment, the postural sway detection devicecomprises a force or balance plate, the force or balance plate includesa force receiving component having a top surface for receiving at leastone portion of the body of the subject; and at least one forcetransducer disposed underneath the force receiving component, and the atleast one force transducer supporting the force receiving component, theat least one force transducer configured to sense one or more measuredquantities and output the one or more second signals, the one or moresecond signals being representative of forces and/or moments beingapplied to the top surface of the force receiving component of the forcemeasurement assembly by the subject, and the at least one forcetransducer comprising a pylon-type force transducer or a forcetransducer beam.

It is to be understood that the foregoing summary and the followingdetailed description of the present invention are merely exemplary andexplanatory in nature. As such, the foregoing summary and the followingdetailed description of the invention should not be construed to limitthe scope of the appended claims in any sense.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will now be described, by way of example, with referenceto the accompanying drawings, in which:

FIG. 1 is a diagrammatic perspective view of a system for measuringpostural sway, eye movement and/or eye position, gaze direction, and/orhead position according to a first embodiment of the invention, whereinthe postural sway detection device is in the form of a force plate;

FIG. 2 is a block diagram of constituent components of the systems ofFIGS. 1 and 8, according to an embodiment of the invention;

FIG. 3 is a block diagram illustrating data manipulation operationscarried out by the force measurement assemblies of the systems of FIGS.1 and 8, according to an embodiment of the invention;

FIG. 4 is a diagrammatic perspective view of one force measurementassembly used in the systems of FIGS. 1 and 8, according to anembodiment of the invention, wherein the force measurement assembly isin the form of a dual force plate;

FIG. 5 is a diagrammatic top view of one force measurement assembly usedin the systems of FIGS. 1 and 8 with exemplary coordinate axessuperimposed thereon, according to an embodiment of the invention,wherein the force measurement assembly is in the form of a dual forceplate;

FIG. 6 is a diagrammatic perspective view of another force measurementassembly used in the systems of FIGS. 1 and 8, according to anembodiment of the invention, wherein the force measurement assembly isin the form of a single force plate;

FIG. 7 is a diagrammatic top view of another force measurement assemblyused in the systems of FIGS. 1 and 8 with exemplary coordinate axessuperimposed thereon, according to an embodiment of the invention,wherein the force measurement assembly is in the form of a single forceplate;

FIG. 8 is a diagrammatic perspective view of a system for measuringpostural sway, eye movement and/or eye position, and gaze directionaccording to a second embodiment of the invention, wherein a visual taskof a dual task protocol is being displayed on the subject visual displaydevice;

FIG. 9 is a diagrammatic frontal view of the subject visual displaydevice of the system of FIG. 8 with a first exemplary visual taskdisplayed thereon, wherein a passage for the subject to read isdisplayed on the screen, according to an embodiment of the invention;

FIG. 10 is a diagrammatic side view of a subject disposed on a surfaceof a force plate, wherein the center of pressure (COP) and the center ofgravity (COG) of the subject are depicted thereon along with thevertical force and shear force components;

FIG. 11 is a free body diagram of a subject illustrating the forcecomponents and parameters that are used in computing center of gravity(COG) of the subject;

FIG. 12 is a trigonometric diagram that is used in computing center ofgravity (COG) of the subject;

FIG. 13 is diagrammatic representation of the output generated by an eyemovement tracking device;

FIG. 14 is diagrammatic representation of a calibration procedurecarried out in conjunction with the eye movement tracking device;

FIG. 15 illustrates exemplary graphs of angular position for a targetand the associated angular position of an eye following the target;

FIG. 16 illustrates exemplary graphs of horizontal position for a targetand the associated horizontal position of an eye following the target,wherein the graphs illustrate a time lag between the horizontal eyeposition and the horizontal target position;

FIG. 17 illustrates exemplary graphs depicting accuracy associated withan eye following a target, wherein both an overshoot condition and anundershoot condition are shown;

FIG. 18A illustrates an exemplary graph of head angular position for asubject test where the head of the subject is moving, but the torso ofthe subject and the target are generally stationary;

FIG. 18B illustrates an exemplary graph of eye angular position for thesubject test where the head of the subject is moving, but the torso ofthe subject and the target are generally stationary;

FIG. 18C illustrates an exemplary graph of gaze angular position for thesubject test where the head of the subject is moving, but the torso ofthe subject and the target are generally stationary;

FIG. 18D illustrates an exemplary graph of target angular position forthe subject test where the head of the subject is moving, but the torsoof the subject and the target are generally stationary;

FIG. 19A illustrates an exemplary graph of head angular position for asubject test where the head, torso, and arms of the subject aregenerally moving in sync with one another and with the target;

FIG. 19B illustrates an exemplary graph of eye angular position for thesubject test where the head, torso, and arms of the subject aregenerally moving in sync with one another and with the target;

FIG. 19C illustrates an exemplary graph of gaze angular position for thesubject test where the head, torso, and arms of the subject aregenerally moving in sync with one another and with the target;

FIG. 19D illustrates an exemplary graph of target angular position forthe subject test where the head, torso, and arms of the subject aregenerally moving in sync with one another and with the target;

FIG. 20 is a diagrammatic perspective view of a system for measuringpostural sway, eye movement and/or eye position, and gaze direction,according to a third embodiment of the invention, wherein the posturalsway detection device is in the form of a plurality of inertialmeasurement units (IMUs);

FIG. 21 is a diagrammatic perspective view of a system for measuringpostural sway, eye movement and/or eye position, and gaze direction,according to a fourth embodiment of the invention, wherein the posturalsway detection device is in the form of a plurality of optical motioncapture devices;

FIG. 22 is a diagrammatic perspective view of a system for measuringpostural sway, eye movement and/or eye position, and gaze direction,according to a fourth embodiment of the invention, wherein the posturalsway detection device is in the form of an infrared motion capturedevice;

FIG. 23 is a diagrammatic perspective view of a system for measuringpostural sway, eye movement and/or eye position, and gaze direction,according to a fifth embodiment of the invention, wherein the eyemovement and eye position tracking device is mounted on an elongatehandle member that is held by the subject; and

FIG. 24 is a diagrammatic perspective view of a system for measuringpostural sway and head position, according to a sixth embodiment of theinvention, wherein head position is displayed on an output screen of avisual display device.

Throughout the figures, the same parts are always denoted using the samereference characters so that, as a general rule, they will only bedescribed once.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

An exemplary embodiment of a system for measuring postural sway, eyemovement and/or eye position, and gaze direction is seen generally at100 in FIG. 1. The system 100 in FIG. 1 generally comprises a forcemeasurement assembly 102 that is operatively coupled to a dataacquisition/data processing device 104 (i.e., a computing device that iscapable of collecting, storing, and processing data), which in turn, isoperatively coupled to an eye movement and eye position tracking device124, and an operator visual display device 156. As illustrated in FIG.1, the force measurement assembly 102 is configured to receive a subject108 thereon, and is capable of measuring the forces and/or momentsapplied to its measurement surfaces 114, 116 by the subject 108.

As shown in FIG. 1, the data acquisition/data processing device 104includes a plurality of user input devices 142, 143 connected thereto.Preferably, the user input devices 142, 143 comprise a keyboard 142 anda mouse 143. In addition, the operator visual display device 156 mayalso serve as a user input device if it is provided with touch screencapabilities. While a desktop type computing system is depicted in FIG.1, one of ordinary of skill in the art will appreciate that another typeof data acquisition/data processing device 104 can be substituted forthe desktop computing system such as, but not limited to, a laptop or apalmtop computing device (i.e., a PDA).

As illustrated in FIG. 1, force measurement assembly 102 is operativelycoupled to the data acquisition/data processing device 104 by virtue ofan electrical cable 118. In one embodiment of the invention, theelectrical cable 118 is used for data transmission, as well as forproviding power to the force measurement assembly 102. Various types ofdata transmission cables can be used for cable 118. For example, thecable 118 can be a Universal Serial Bus (USB) cable or an Ethernetcable. Preferably, the electrical cable 118 contains a plurality ofelectrical wires bundled together, with at least one wire being used forpower and at least another wire being used for transmitting data. Thebundling of the power and data transmission wires into a singleelectrical cable 118 advantageously creates a simpler and more efficientdesign. In addition, it enhances the safety of the testing environmentwhen human subjects are being tested on the force measurement assembly102. However, it is to be understood that the force measurement assembly102 can be operatively coupled to the data acquisition/data processingdevice 104 using other signal transmission means, such as a wirelessdata transmission system. If a wireless data transmission system isemployed, it is preferable to provide the force measurement assembly 102with a separate power supply in the form of an internal power supply ora dedicated external power supply.

Referring again to FIG. 1, it can be seen that the force measurementassembly 102 of the illustrated embodiment is in the form of a dualforce plate assembly. The dual force plate assembly includes a firstplate component 110, a second plate component 112, at least one forcetransducer associated with the first plate component 110, and at leastone force transducer associated with the second plate component 112. Inthe illustrated embodiment, a subject 108 stands in an upright positionon the force measurement assembly 102 and each foot of the subject 108is placed on the top surfaces 114, 116 of a respective plate component110, 112 (i.e., one foot on the top surface 114 of the first platecomponent 110 and the other foot on the top surface 116 of the secondplate component 112). The at least one force transducer associated withthe first plate component 110 is configured to sense one or moremeasured quantities and output one or more first signals that arerepresentative of forces and/or moments being applied to its measurementsurface 114 by the left foot/leg 108 a of the subject 108, whereas theat least one force transducer associated with the second plate component112 is configured to sense one or more measured quantities and outputone or more second signals that are representative of forces and/ormoments being applied to its measurement surface 116 by the rightfoot/leg 108 b of subject 108.

In the illustrated embodiment, the at least one force transducerassociated with the first and second plate components 110, 112 comprisesfour (4) pylon-type force transducers 160 (or pylon-type load cells)that are disposed underneath, and near each of the four corners (4) ofthe first plate component 110 and the second plate component 112 (seeFIG. 4). Each of the eight (8) illustrated pylon-type force transducers160 has a plurality of strain gages adhered to the outer periphery of acylindrically-shaped force transducer sensing element for detecting themechanical strain of the force transducer sensing element impartedthereon by the force(s) applied to the surfaces of the force measurementassembly 102. As shown in FIG. 4, a base plate 200 can be providedunderneath the transducers 160 of each plate component 110, 112. In someembodiments, the feet 126 are mounted on the bottom surface of this baseplate 200. Also, in some embodiments, side plates are mounted betweenthe base plate 200 and the plate components 110, 112 so as to concealthe force transducers 160.

In an alternative embodiment, rather than using four (4) pylon-typeforce transducers 160 on each plate component 110, 112, forcetransducers in the form of transducer beams could be provided under eachplate component 110, 112. In this alternative embodiment, the firstplate component 110 could comprise two transducer beams that aredisposed underneath, and on generally opposite sides of the first platecomponent 110. Similarly, in this embodiment, the second plate component112 could comprise two transducer beams that are disposed underneath,and on generally opposite sides of the second plate component 112.Similar to the pylon-type force transducers 160, the force transducerbeams could have a plurality of strain gages attached to one or moresurfaces thereof for sensing the mechanical strain imparted on the beamby the force(s) applied to the surfaces of the force measurementassembly 102.

Rather, than using four (4) force transducer pylons under each plate, ortwo spaced apart force transducer beams under each plate, it is to beunderstood that the force measurement assembly 102 can also utilize theforce transducer technology described in U.S. Pat. No. 8,544,347, theentire disclosure of which is incorporated herein by reference.

Also, as shown in FIG. 1, the force measurement assembly 102 is providedwith a plurality of support feet 126 disposed thereunder. Preferably,each of the four (4) corners of the force measurement assembly 102 isprovided with a support foot 126. In some embodiment(s), each supportfoot 126 is attached to a bottom surface of a force transducer or a baseplate. In another embodiment, one or more of the force transducers couldfunction as support feet (e.g., if pylon-type force transducers areused, the first and second plate components 110, 112 could be supportedon the force transducers). In one preferred embodiment, at least one ofthe support feet 126 is adjustable so as to facilitate the leveling ofthe force measurement assembly 102 on an uneven floor surface.

Now, turning to FIG. 2, it can be seen that the data acquisition/dataprocessing device 104 of the system 100 of FIG. 1 comprises amicroprocessor 104 a for processing data, memory 104 b (e.g., randomaccess memory or RAM) for storing data during the processing thereof,and data storage device(s) 104 c, such as one or more hard drives,compact disk drives, floppy disk drives, flash drives, or anycombination thereof. As shown in FIG. 2, the force measurement assembly102, the eye movement and eye position tracking device 124, and theoperator visual display device 156 are operatively coupled to the dataacquisition/data processing device 104 such that data is capable ofbeing transferred between these devices 102, 104, 124, and 156. Also, asillustrated in FIG. 2, a plurality of user data input devices, such as akeyboard 142 and a mouse 143, are operatively coupled to the dataacquisition/data processing device 104 so that a user is able to enterdata into the data acquisition/data processing device 104. In someembodiments, the data acquisition/data processing device 104 can be inthe form of a desktop computer, while in other embodiments, the dataacquisition/data processing device 104 can be embodied as a laptopcomputer.

With reference to FIG. 1, the operator visual display device 156 of thesystem 100 will be described in more detail. In the illustratedembodiment, the operator visual display device 156 is in the form of aflat panel monitor. The operator visual display device 156 isoperatively coupled to the data acquisition/data processing device 104by means of data transmission cable 158. Those of ordinary skill in theart will readily appreciate that various types of flat panel monitorshaving various types of data transmission cables 158 may be used tooperatively couple the operator visual display device 156 to the dataacquisition/data processing device 104. For example, the flat panelmonitor employed may utilize a video graphics array (VGA) cable, adigital visual interface (DVI or DVI-D) cable, a high-definitionmultimedia interface (HDMI or Mini-HDMI) cable, or a DisplayPort digitaldisplay interface cable to connect to the data acquisition/dataprocessing device 104. Alternatively, in other embodiments of theinvention, the operator visual display device 156 can be operativelycoupled to the data acquisition/data processing device 104 usingwireless data transmission means. Electrical power is supplied to theoperator visual display device 156 using a separate power cord thatconnects to a building wall receptacle.

Those of ordinary skill in the art will appreciate that the operatorvisual display device 156 can be embodied in various forms. For example,if the operator visual display device 156 is in the form of a flatscreen monitor as illustrated in FIG. 1, it may comprise a liquidcrystal display (i.e., an LCD display), a light-emitting diode display(i.e., an LED display), a plasma display, a projection-type display, ora rear projection-type display. The operator visual display device 156may also be in the form of a touch pad display.

FIG. 3 graphically illustrates the acquisition and processing of theload data carried out by the exemplary embodiment of the system 100 ofFIG. 1. Initially, as shown in FIG. 3, a load L is applied to the forcemeasurement assembly 102 by a subject disposed thereon. The load istransmitted from the first and second plate components 110, 112 to itsrespective set of pylon-type force transducers 160 or force transducerbeams. As described above, in one embodiment of the invention, eachplate component 110, 112 comprises four (4) pylon-type force transducers160 disposed thereunder (e.g., see FIG. 4). Preferably, these pylon-typeforce transducers are disposed near respective corners of each platecomponent 110, 112. In a preferred embodiment of the invention, each ofthe pylon-type force transducers 160 includes a plurality of straingages wired in one or more Wheatstone bridge configurations, wherein theelectrical resistance of each strain gage is altered when the associatedportion of the associated pylon-type force transducer undergoesdeformation (i.e., a measured quantity) resulting from the load (i.e.,forces and/or moments) acting on the first and second plate components110, 112. For each plurality of strain gages disposed on the pylon-typeforce transducers 160, the change in the electrical resistance of thestrain gages brings about a consequential change in the output voltageof the Wheatstone bridge (i.e., a quantity representative of the loadbeing applied to the measurement surface). Thus, in one embodiment, thefour (4) pylon-type force transducers 160 disposed under each platecomponent 110, 112 output a total of four (4) analog output voltages(signals). In another embodiment, the four (4) pylon-type forcetransducers 160 disposed under each plate component 110, 112 output acombined total of three (3) analog output voltages (signals). In someembodiments, the three (3) or four (4) analog output voltages from eachplate component 110, 112 are then transmitted to a preamplifier board(not shown) for preconditioning. The preamplifier board is used toincrease the magnitudes of the transducer analog voltages, andpreferably, to convert the analog voltage signals into digital voltagesignals as well. After which, the force measurement assembly 102transmits the force plate output signals S_(FPO1)-S_(FPO8) to a mainsignal amplifier/converter 144. Depending on whether the preamplifierboard also includes an analog-to-digital (A/D) converter, the forceplate output signals S_(FPO1)-S_(FPO8) could be either in the form ofanalog signals or digital signals. The main signal amplifier/converter144 further magnifies the force plate output signals S_(FPO1)-S_(FPO8),and if the signals S_(FPO1)-S_(FPO8) are of the analog-type (for a casewhere the preamplifier board did not include an analog-to-digital (A/D)converter), it may also convert the analog signals to digital signals.Then, the signal amplifier/converter 144 transmits either the digital oranalog signals S_(ACO1)-S_(ACO8) to the data acquisition/data processingdevice 104 (computer or computing device 104) so that the forces and/ormoments that are being applied to the surfaces of the force measurementassembly 102 can be transformed into output values OV that can be usedto determine the postural sway of the subject 108. In addition to thecomponents 104 a, 104 b, 104 c, the data acquisition/data processingdevice 104 may further comprise an analog-to-digital (A/D) converter ifthe signals S_(ACO1)-S_(ACO8) are in the form of analog signals. In sucha case, the analog-to-digital converter will convert the analog signalsinto digital signals for processing by the microprocessor 104 a.

When the data acquisition/data processing device 104 receives thevoltage signals S_(ACO1)-S_(ACO8), it initially transforms the signalsinto output forces and/or moments by multiplying the voltage signalsS_(ACO1)-S_(ACO8) by a calibration matrix. After which, the force F_(L)exerted on the surface of the first force plate by the left foot of thesubject, the force F_(R) exerted on the surface of the second forceplate by the right foot of the subject, and the center of pressure foreach foot of the subject (i.e., the x and y coordinates of the point ofapplication of the force applied to the measurement surface by eachfoot) are determined by the data acquisition/data processing device 104.The computations performed in the determination of the forces and centerof pressure are described hereinafter.

While, in one exemplary embodiment described hereinafter, the dataacquisition/data processing device 104 determines the vertical forcesF_(Lz), F_(Rz) exerted on the surface of the first and second forceplates by the feet of the subject and the center of pressure for eachfoot of the subject, it is to be understood that the invention is not solimited. Rather, in other embodiments of the invention, the outputforces of the data acquisition/data processing device 104 could includeall three (3) orthogonal components of the resultant forces acting onthe two plate components 110, 112. In yet other embodiments of theinvention, the output forces and moments of the data acquisition/dataprocessing device 104 can be in the form of other forces and moments aswell.

Referring again to FIG. 1, it can be seen that the subject 108 is alsoprovided with the eye movement and eye position tracking device 124 thatis configured to track the eye movement and eye position of the subject108 while he performs a balance test and/or a concussion screening test.In the illustrated embodiment, the eye movement and eye positiontracking device 124 is used in conjunction with the postural swaydetection device (i.e., force plate 102). The eye movement and eyeposition tracking device 124 may incorporate one or more video camerasfor capturing an image of one of the subject's eye or images of both ofthe subject's eyes (i.e., one camera dedicated to each one of thesubject's eyes). In one or more embodiments, the video cameras of theeye movement and eye position tracking device 124 may comprise infraredcameras in order to enable accurate images of the eye to be capturedeven in low light environments. The one or more video cameras of the eyemovement and eye position tracking device 124 may capture at least sixty(60) frames per second. In one or more embodiments, only approximately aquarter of the pixels in each image captured by the one or more camerasmay be downloaded (i.e., the part of the image centered around the eye)in order to increase the minimum resolution of the camera to 250 framesper second (i.e., 250 Hz) by decreasing the image size being downloadedby approximately one-quarter. In an alternative embodiment, the eyemovement and eye position tracking device 124 may be in the form of theeye movement tracking devices described in U.S. Pat. Nos. 6,113,237 and6,152,564, the entire disclosures of which are incorporated herein byreference. The eye movement and eye position tracking device 124 isconfigured to output one or more signals that are representative of thedetected eye movement and position of the subject 108 (e.g., the slowand fast eye movements of the subject). As explained above, the eyemovement and eye position tracking device 124 may be operativelyconnected to the data acquisition/data processing device 104 for datacollection and analysis of the eye movement and position data acquiredby the eye movement and eye position tracking device 124 (e.g., by usingwireless data transmission means). As such, using the output signalsfrom the eye movement and eye position tracking device 124, the dataacquisition/data processing device 104 may be specially programmed todetermine the eye movement and position of the subject 108 during theperformance of the balance test and/or the concussion screening test.

Now, the functionality of the system 100 for measuring postural sway,eye movement and/or eye position, and gaze direction will be describedin detail. It is to be understood that the aforedescribed functionalityof the system 100 of FIG. 1 can be carried out by the dataacquisition/data processing device 104 utilizing software, hardware, ora combination of both hardware and software. For example, the dataacquisition/data processing device 104 can be specially programmed tocarry out the functionality described hereinafter. In one embodiment ofthe invention, the computer program instructions necessary to carry outthis functionality may be loaded directly onto an internal data storagedevice 104 c of the data acquisition/data processing device 104 (e.g.,on a hard drive thereof) and subsequently executed by the microprocessor104 a of the data acquisition/data processing device 104. Alternatively,these computer program instructions could be stored on a portablecomputer-readable medium (e.g., a flash drive, a floppy disk, a compactdisk, etc.), and then subsequently loaded onto the data acquisition/dataprocessing device 104 such that the instructions can be executedthereby. In other embodiments, these computer program instructions couldbe embodied in the hardware of the data acquisition/data processingdevice 104, rather than in the software thereof. It is also possible forthe computer program instructions to be embodied in a combination ofboth the hardware and the software.

In the illustrated embodiment, the data acquisition/data processingdevice 104 is configured to compute the postural sway of the subject108. As described above, when the data acquisition/data processingdevice 104 receives the voltage signals S_(ACO1)-S_(ACO6), it initiallytransforms the signals into output forces and/or moments by multiplyingthe voltage signals S_(ACO1)-S_(ACO6) by a calibration matrix (e.g.,F_(Lz), M_(Lx), M_(Ly), F_(Rz), M_(Rx), M_(Ry)). After which, the centerof pressure for each foot of the subject (i.e., the x and y coordinatesof the point of application of the force applied to the measurementsurface by each foot) are determined by the data acquisition/dataprocessing device 104. Referring to FIG. 5, which depicts a top view ofthe measurement assembly 102, it can be seen that the center of pressurecoordinates (x_(P) _(L) , y_(PD) _(L) ) for the first plate component110 are determined in accordance with x and y coordinate axes 130, 132.Similarly, the center of pressure coordinates (x_(P) _(R) , y_(P) _(R) )for the second plate component 112 are determined in accordance with xand y coordinate axes 134, 136. If the force transducer technologydescribed in U.S. Pat. No. 8,544,347 is employed, it is to be understoodthat the center of pressure coordinates (x_(P) _(L) , y_(P) _(L) , x_(P)_(R) , x_(P) _(R) ) can be computed in the particular manner describedin that patent.

As explained above, rather than using a force measurement assembly 102having first and second plate components 110, 112, a force measurementassembly 102′ in the form of a single force plate may be employed (seeFIGS. 6 and 7, which illustrate a single force plate). Similar to thatdescribed above for the dual force plate of FIG. 4, a base plate 200′can be provided underneath the transducers 160 of the single force plateillustrated in FIG. 6. Unlike the dual force plate assembly illustratedin FIG. 4, the single force plate comprises a single measurement surfaceon which both of a subject's feet are placed during testing. As such,rather than computing two sets of center of pressure coordinates (i.e.,one for each foot of the subject), the embodiments employing the singleforce plate compute a single set of overall center of pressurecoordinates (x_(P), y_(P)) in accordance with x and y coordinate axes150, 152. The manner in which the center of pressure coordinates arecomputed for the single force plate assembly is the same as thatdescribed above for a single plate of the dual force plate assembly,except that there will only be a single set of center of pressurecoordinates (e.g., coordinates x_(P), y_(P)) for a single measurementsurface, rather than two sets of coordinates (x_(P) _(L) , y_(P) _(L) ;x_(P) _(R) , y_(P) _(R) ) described above for the two independentmeasurement surfaces 114, 116 of the dual force plate assembly.

In one exemplary embodiment, the data acquisition/data processing device104 determines the vertical forces F_(Lz), F_(Rz) exerted on the surfaceof the first and second force plates by the feet of the subject and thecenter of pressure for each foot of the subject, while in anotherexemplary embodiment, the output forces of the data acquisition/dataprocessing device 104 include all three (3) orthogonal components of theresultant forces acting on the two plate components 110, 112 (i.e.,F_(Lx), F_(Ly), F_(Lz), F_(Rx), F_(Ry), F_(Rz)) and all three (3)orthogonal components of the moments acting on the two plate components110, 112 (i.e., M_(Lx), M_(Ly), M_(Lz), M_(Rx), M_(Ry), M_(Rz)). In yetother embodiments of the invention, the output forces and moments of thedata acquisition/data processing device 104 can be in the form of otherforces and moments as well.

In the exemplary embodiments where only the vertical forces F_(Lz),F_(Rz) are determined, the one or more numerical values determined fromthe output signals of the force transducers associated with the firstplate component 110 may include x and y coordinates (e.g., coordinatesx_(P) _(L) , y_(P) _(L) ) specifying the center of pressure of a firstforce vector (e.g., left force vector F_(L)) applied by the subject tothe first measurement surface 114 of the first plate component 110(e.g., left plate) by the subject. Similarly, the one or more numericalvalues determined from the output signals of the force transducersassociated with the second plate component 112 further include x and ycoordinates (e.g., coordinates x_(P) _(R) , y_(P) _(R) ) specifying thecenter of pressure of a second force vector (e.g., right force vector{right arrow over (F)}_(R)) applied by the subject to the secondmeasurement surface 116 of the second plate component 112 (e.g., rightplate) by the subject. If the left and right force plates of the forcemeasurement assembly 102 are configured as 3-component force measurementdevices (i.e., the transducers of these plates are capable ofcollectively measuring F_(Z), M_(x), M_(y)), then the center of pressureof the first force vector {right arrow over (F)}_(L) applied by thesubject to the first measurement surface 114 of the first platecomponent 110 is computed as follows:

$\begin{matrix}{x_{P_{L}} = \frac{- M_{y_{L}}}{F_{Z_{L}}}} & (1) \\{y_{P_{L}} = \frac{M_{x_{L}}}{F_{Z_{L}}}} & (2)\end{matrix}$where:x_(P) _(L) , y_(P) _(L) : coordinates of the point of application forthe force (i.e., center of pressure) on the first plate component 110(left force plate);F_(Z) _(L) : z-component of the resultant force acting on the firstplate component 110 (left force plate);M_(x) _(L) : x-component of the resultant moment acting on the firstplate component 110 (left force plate); andM_(y) _(L) : y-component of the resultant moment acting on the firstplate component 110 (left force plate).

Similarly, when the left and right force plates of the force measurementassembly 102 are configured as 3-component force measurement devices,the center of pressure of the second force vector {right arrow over(F)}_(R) applied by the subject to the second measurement surface 116 ofthe second plate component 112 is computed as follows:

$\begin{matrix}{x_{P_{R}} = \frac{- M_{y_{R}}}{F_{Z_{R}}}} & (3) \\{y_{P_{R}} = \frac{M_{x_{R}}}{F_{Z_{R}}}} & (4)\end{matrix}$x_(P) _(R) , y_(P) _(R) : coordinates of the point of application forthe force (i.e., center of pressure) on the second plate component 112(right force plate);F_(Z) _(R) : z-component of the resultant force acting on the secondplate component 112 (right force plate);M_(x) _(R) : x-component of the resultant moment acting on the secondplate component 112 (right force plate); andM_(y) _(R) : y-component of the resultant moment acting on the secondplate component 112 (right force plate).

However, if the left and right force plates of the force measurementassembly 102 are configured as 6-component force measurement devices(i.e., the transducers of these plates are capable of collectivelymeasuring F_(x), F_(y), F_(z), M_(x), M_(y), M_(z)), then the center ofpressure of the first force vector {right arrow over (F)}_(L) applied bythe subject to the first measurement surface 114 of the first platecomponent 110 is computed as follows:

$\begin{matrix}{x_{P_{L}} = \frac{{{- h_{L}} \cdot F_{x_{L}}} - M_{y_{L}}}{F_{z_{L}}}} & (5) \\{y_{P_{L}} = \frac{{{- h_{L}} \cdot F_{y_{L}}} + M_{x_{L}}}{F_{z_{L}}}} & (6)\end{matrix}$where:h_(L): thickness above the top surface of any material covering thefirst plate component 110 (left force plate);F_(x) _(L) : x-component of the resultant force acting on the firstplate component 110 (left force plate); andF_(y) _(L) : y-component of the resultant force acting on the firstplate component 110 (left force plate).

Similarly, when the left and right force plates of the force measurementassembly 102 are configured as 6-component force measurement devices,the center of pressure of the second force vector {right arrow over(F)}_(R) applied by the subject to the second measurement surface 116 ofthe second plate component 112 is computed as follows:

$\begin{matrix}{x_{P_{R}} = \frac{{{- h_{R}} \cdot F_{x_{R}}} - M_{y_{R}}}{F_{z_{R}}}} & (7) \\{y_{P_{R}} = \frac{{{- h_{R}} \cdot F_{y_{R}}} + M_{x_{R}}}{F_{z_{R}}}} & (8)\end{matrix}$where:h_(R): thickness above the top surface of any material covering thesecond plate component 112 (right force plate);F_(x) _(R) : x-component of the resultant force acting on the secondplate component 112 (right force plate); andF_(y) _(R) : y-component of the resultant force acting on the secondplate component 112 (right force plate).

In an exemplary embodiment where only the single force plate of FIGS. 6and 7 is utilized, and only the vertical force F_(z) is determined, theone or more numerical values determined from the output signals of theforce transducers associated with the force plate 102′ may include x andy coordinates (e.g., coordinates x_(P), y_(P)) specifying the center ofpressure of a force vector (e.g., a force vector {right arrow over (F)})applied by the subject to the single measurement surface of the singleforce plate 102′. Also, if the force plate 102′ is configured as a3-component force measurement device (i.e., the transducers of thisplate are capable of collectively measuring F_(Z), M_(x), M_(y)), thenthe center of pressure of the force vector {right arrow over (F)}applied by the subject to the measurement surface of the force plate102′ is computed as follows:

$\begin{matrix}{x_{P} = \frac{- M_{Y}}{F_{Z}}} & (9) \\{y_{P} = \frac{M_{X}}{F_{Z}}} & (10)\end{matrix}$where:x_(P), y_(P): coordinates of the point of application for the force(i.e., center of pressure) on the single force plate 102′;F_(Z): z-component of the resultant force acting on the single forceplate 102′;M_(x): x-component of the resultant moment acting on the single forceplate 102′; andM_(y): y-component of the resultant moment acting on the single forceplate 102′.

In one or more embodiments, the data acquisition/data processing device104 may convert the computed center of pressure (COP) to a center ofgravity (COG) for the subject using a Butterworth filter. For example,in one exemplary, non-limiting embodiment, a second-order Butterworthfilter with a 0.75 Hz cutoff frequency is used. In addition, the dataacquisition/data processing device 104 also computes a sway angle forthe subject using a corrected center of gravity (COG′) value, whereinthe center of gravity (COG) value is corrected to accommodate for theoffset position of the subject relative to the origin of the coordinateaxes (130, 132, 134, 136) of the force plate assembly 102 or the offsetposition of the subject relative to the origin of the coordinate axes(150, 152) of the force plate assembly 102′. For example, the dataacquisition/data processing device 104 computes the sway angle for thesubject in the following manner:

$\begin{matrix}{\theta = {{\sin^{- 1}\left( \frac{C\; O\; G^{\prime}}{0.55h} \right)} - {2.3{^\circ}}}} & (11)\end{matrix}$where:θ: sway angle of the subject;COG′: corrected center of gravity of the subject; andh: height of the center of gravity of the subject.

In one or more other alternative embodiments, the data acquisition/dataprocessing device 104 may directly calculate the center of gravity forthe subject. Initially, referring to FIG. 10, a side view of a subject108′ disposed on a surface of a force plate 102 is diagrammaticallyillustrated. As shown in this figure, the ground reaction force vector{right arrow over (F)} passes through the center of pressure (COP) forthe subject and the subject's center of gravity (COG). For the purposeof the analysis, the ground reaction force vector {right arrow over (F)}can be represented by its constituent components, namely its verticalforce component F_(Z) and its shear force component F_(Y). It is to benoted that, for the purposes of this analysis, only the sagittal planeof the subject is being considered.

Then, with reference to FIG. 11, it can be seen that the y-coordinate(y) of the subject's center-of-gravity is the unknown parameter beingcomputed by the data acquisition/data processing device 104. The centerof pressure (COP) y-coordinate (y₀) is known from the force plate output(e.g., refer to the calculations described above). Also, as shown inFIG. 11, the following trigonometric relationship exists between theangle θ, the vertical force component F_(Z), and the shear forcecomponent F_(Y):

$\begin{matrix}{{\tan\theta} = \frac{F_{Z}}{F_{Y}}} & (12)\end{matrix}$Now, turning to FIG. 12, it can be seen that the tangent of the angle θis also equal to the following:

$\begin{matrix}{{\tan\theta} = \frac{{0.5}5H}{y - y_{0}}} & (13)\end{matrix}$where:

-   -   H: height of the subject;    -   y: y-coordinate of the center of gravity (COG) of the subject;        and    -   y₀: y-coordinate of the center of pressure (COP) of the subject        determined from the force plate output.

Thus, it follows that equations (12) and (13) can be combined to obtainthe following relationship:

$\begin{matrix}{\frac{{0.5}5H}{y - y_{0}} = \frac{F_{Z}}{F_{Y}}} & (14)\end{matrix}$This equation (14) can be initially rearranged as follows:

$\begin{matrix}{{y - y_{0}} = {\frac{F_{Y}}{F_{Z}}\left( {{0.5}5H} \right)}} & (15)\end{matrix}$Finally, to solve for the unknown y-coordinate (y) of the subject'scenter of gravity, equation (15) is rearranged in the following manner:

$\begin{matrix}{y = {y_{0} + {\frac{F_{Y}}{F_{Z}}\left( {{0.5}5H} \right)}}} & (16)\end{matrix}$Therefore, the y-coordinate (y) of the subject's center of gravity canthen be determined as a function of the y-coordinate (y₀) of thesubject's center of pressure, the shear force component F_(Y), thevertical force component F_(Z), and the height of the subject H. They-coordinate (y₀) of the subject's center of pressure, the shear forcecomponent F_(Y), and the vertical force component F_(Z) are alldetermined from the output of the force plate, whereas the height of thesubject can be entered into the data acquisition/data processing device104 by the user of the system (i.e., after the system user acquires theheight value from the subject being tested). Advantageously, thecomputational method described above enables the subject's center ofgravity to be accurately determined using the force measurement system.

In one or more embodiments, a method for concurrently measuring the eyemovement and/or eye position and postural sway of a subject is performedusing the system illustrated in FIG. 1. Initially, the subject 108 ispositioned in an upright position on a surface or surfaces (e.g., thefirst and second measurement surfaces 114, 116 of the dual force plate102 in FIG. 1). Then, the eye movement and eye position of the subject108 is measured using the eye movement tracking device 124. The eyemovement tracking device 124 outputs one or more first signals that arerepresentative of the detected eye movement and eye position of thesubject 108 to the data acquisition/data processing device 104. Inaddition, the postural sway of the subject 108 is measured using apostural sway detection device (i.e., the force plate 102 in FIG. 1)while the eye movement and eye position of the subject 108 issimultaneously measured by the eye movement tracking device 124. Thepostural sway detection device (i.e., force plate 102) outputs the oneor more second signals that are representative of the postural sway ofthe subject to the data acquisition/data processing device 104. Afterwhich, the data acquisition/data processing device 104 is speciallyprogrammed to determine the eye movement and eye position data for thesubject 108 from the one or more first signals output by the eyemovement tracking device 124. The data acquisition/data processingdevice 104 also is specially programmed to determine postural sway datafor the subject 108 from the one or more second signals output by thepostural sway detection device (i.e., force plate 102).

Next, an illustrative manner in which the data acquisition/dataprocessing device 104 of the system 100 in FIG. 1 performs the eyemovement and eye position calculations will be explained in detail.Referring to FIG. 13, it can be seen that the eye movement trackingdevice 124 comprises one or more cameras 138 (e.g., two cameras, one foreach eye of the subject) Each of the one or more cameras 138 captures atime-stamped image 140 of a respective eye 146 of the subject 108. Forexample, in one or more embodiments, the location of the pupil 147 ofthe eye 146 may be extracted from a grayscale image 140. Because thepupil is darker than the remainder of the image (i.e., the pupil isgenerally black in a grayscale image), its location is easily extractedfrom the camera image 140. The location of the pupil 147 of the eye 146is defined in terms of pupil coordinates within the image 140 (i.e., thepupil coordinates may correspond to the pixel coordinates of the image).As shown in FIG. 13, using the information from the time-stamped image140, the data acquisition/data processing device 104 may generate outputdata 148 that includes the x, y, and z coordinates of the center pointof the pupil 147 of the eye 146 and the time at which the image 140 wastaken. The x and y coordinates of the center point of the pupil 147represent its horizontal and vertical positions in the image 140,respectively, while the z coordinate is the torsional coordinate thatrepresents the angular position of the subject's eyeball in the eyesocket of the subject 108.

With reference to FIG. 14, an illustrative calibration procedure forcorrelating the eye position of the subject 108 within the eye image140′ with an angular position of the eye will be described. In FIG. 14,a subject visual display device 106 is depicted on the left side of thisfigure, while an eye image 140′ is depicted on the right side of thisfigure. For the sake of clarity, the image of the actual eye has beenexcluded from the eye image 140′, and the position of the pupil of thesubject's eye is represented by a single point 154. As shown on the leftside of FIG. 14, the subject visual display device 106 comprises ascreen image 162 with a plurality of points arranged in a grid pattern.In the screen image 162, the center point 164 corresponds to a zeroangular position in both the horizontal and vertical directions (i.e.,0°, 0°). The top row of points in the screen image 162 each have avertical angular position of 20 degrees, the middle row of points eachhave a vertical angular position of 0 degrees, and the bottom row ofpoints each have a vertical angular position of −20 degrees. Theleftmost column of points in the screen image 162 each have a horizontalangular position of −30 degrees, the middle column of points each have ahorizontal angular position of 0 degrees, and the rightmost column ofpoints each have a horizontal angular position of 30 degrees. Initially,during the calibration procedure, the subject 108 may be instructed tofocus on the center point 164 (i.e., the 0°, 0° point) in the screenimage 162, which is correlated with the center position of the subject'seye in the eye image 140′ (i.e., with pixel coordinates 100, 100). Then,during the calibration procedure, the subject 108 may be instructed tofocus on the point 166 (i.e., the −30°, 0° point) in the screen image162, which is correlated with the point 154 in the eye image 140′ (i.e.,with pixel coordinates 50, 100) representing the center point of thepupil of the subject's eye. In this manner, as the subject 108 isinstructed to focus on each of the nine points in the screen image 162of FIG. 14, the coordinates representing the center point of the pupilof the subject's eye are correlated with the angular position of thesubject's eye in both the horizontal and vertical directions. As such,during the tests described hereinafter, once the coordinate of thesubject's eye is determined, the angular position of the subject's eyemay be easily determined using the results of the calibration proceduredescribed above.

After the data acquisition/data processing device 104 determines the eyemovement and eye position data and the postural sway data for thesubject 108, the data acquisition/data processing device 104 may bespecially programmed to further determine a first numerical score forthe subject 108 based upon the eye movement and eye position data, and asecond numerical score for the subject 108 based upon the postural swaydata. Then, the data acquisition/data processing device 104 may bespecially programmed to combine the first numerical score with thesecond numerical score to obtain an overall combined sway and eyemovement score for the subject.

Similarly, after the data acquisition/data processing device 104determines the eye movement and eye position data and the postural swaydata for the subject 108, the data acquisition/data processing device104 may be specially programmed to determine one or more eye movementdeviation values based upon the eye movement and eye position datadetermined for the subject 108. The one or more eye movement deviationvalues quantify instances during the balance test and/or the concussionscreening test where the subject is unable to follow a particulartarget. The data acquisition/data processing device 104 may be speciallyprogrammed to further determine a balance sway score for the subject 108based upon the postural sway data determined for the subject 108, andthen compute an adjusted balance sway score for the subject 108 byincreasing the balance sway score determined for the subject 108 by anumerical factor proportionate to the one or more eye movement deviationvalues.

For example, in an illustrative embodiment, a balance sway score of thesubject 108 may comprise one of the following: (i) a maximum sway ofcenter-of-pressure (COP) (e.g., plus or minus 15 millimeters), (ii) amaximum sway of center-of-gravity (COG) about the ankle (e.g., plus orminus 7 degrees), and (iii) an area of ellipse fitted around the path ofthe COP with, for example, a 90 percent confidence area (e.g., 4.0 sq.centimeters). In the illustrative embodiment, the eye score of thesubject 108 may comprise a measurement of how far behind the eyes lagthe target (e.g., 10 degrees). Considering the above examples, anillustrative combined sway and eye movement score of the subject 108 maycomprise one of the following: (i) a balance sway score of 15millimeters multiplied by the eye score of 10 degrees so as to obtain acombined sway and eye movement score of 150 (i.e., 15×10), (ii) abalance sway score of 7 degrees multiplied by the eye score of 10degrees so as to obtain a combined sway and eye movement score of 70(i.e., 7×10), and (iii) a balance sway score of 4.0 sq. centimetersmultiplied by the eye score of 10 degrees so as to obtain a combinedsway and eye movement score of 40 (i.e., 4×10), depending on which ofthe above balance scoring techniques is utilized. The final scoreresult(s) may be compared with the score for a normal subject. When oneor more of the individual scores or their product (as illustrated above)is not normal, this may be indicative of a possible concussion.

In an alternative illustrative embodiment, the eye movements of thesubject 108 may be defined by the ratio of peak eye velocity to peaktarget velocity (i.e., gain). For example, when the subject 108 is ableto track the target perfectly, the gain will be close to 1.0 (e.g.,between 0.9 and 1.0). Conversely, when the subject is unable to trackthe target, the gain will be closer to zero (e.g., between 0.1 and 0.2).In addition, in this illustrative embodiment, fast eye movements may becharacterized based on their accuracy, velocity, and latency (i.e., thetime required to initiate eye movements). For example, the numbers for anormal subject are: 90% accuracy, 400 deg/sec velocity, and 200millisecond latency. All of these values may be summarized in a singlenumber (i.e., a hybrid value) to quantify the eye movements. In thisillustrative embodiment, when the raw gain is used as the eye score forthe subject 108, the eye score decreases with increased abnormality.Although, in order for the eye score to increase with increasedabnormality, the inverse of the gain may be used in lieu of the raw gain(e.g., 1/0.1 produces a larger eye score than 1/0.9). Also, when theinverse of the gain is used for the eye score, the product of anabnormal balance sway score and an abnormal eye score results in alarger combined sway and eye movement score, as described in theillustrative embodiment described above. As such, subjects or patientswho are concussed would have a higher combined sway and eye movementscore than subjects or patients who are not concussed.

With reference to FIG. 15, an exemplary manner for determining the gainfor eye movements of the subject 108 will be described. In FIG. 15, thetop sinusoidal curve 168 represents angular position of the target(θ_(T)) over time, whereas the bottom sinusoidal curve 172 representsangular position of the subject's eye (θ_(E)) over time. The gain for asubject 108 is computed by determining the peak target velocity from thepeak slope 170 of the curve 168 (i.e. computing the derivative of thecurve 168 at its peak slope location), and by determining the peak eyevelocity from the peak slope 174 of the curve 172 (i.e. computing thederivative of the curve 172 at its peak slope location). Then, the gainvalue is determined by computing the ratio of the peak eye velocity tothe peak target velocity.

Next, referring to FIG. 16, an exemplary manner for determining thelatency or time lag for eye movements of the subject 108 will bedescribed. In FIG. 16, the top curve or function 176 represents thehorizontal position of the target over time (i.e., the x coordinateposition of the target over time), whereas the bottom curve or function178 represents the horizontal position of the subject's eye over time(i.e., the x coordinate position of the subject's eye over time). Asshown in FIG. 16, the target and the subject's eye generally movebetween a first position (P1) and a second position (P2). During the eyetest that generates the curves 176, 178, the subject 108 is instructedto follow the target with his or her eyes as closely as possible. InFIG. 16, it can be seen that the subject's eye lags behind the target inmoving from the first position (P1) to the second position (P2) by atime lag amount (t₁) 180. In other words, it takes the subject's eye acertain amount of time (t₁) to start moving after the target has alreadystarting moving (i.e., the subject's eye is unable to reactinstantaneously to the movement of the target). The subject's time lag180 is computed by comparing the target position curve 176 to the eyeposition curve 178.

Turning to FIG. 17, an exemplary manner for determining the accuracy ofeye movements by the subject 108 will be explained. In the graphs ofFIG. 17, the dashed line curve or function 182 represents the horizontalposition of the target over time (i.e., the x coordinate position of thetarget over time), whereas the solid line curves or functions 184, 186represent the horizontal position of the subject's eye over time (i.e.,the x coordinate position of the subject's eye over time). As shown inFIG. 17, the target and the subject's eye generally move between a firstposition (P1) and a second position (P2). During the eye test thatgenerates the curves 182, 184, 186, the subject 108 is instructed totrack the target with his or her eyes as closely as possible. The topgraph of FIG. 17 illustrates an overshoot condition where the subjectinitially overshoots the second position (P2) of the target with his orher eyes (e.g., the subject overshoots the target by 120%). Conversely,the bottom graph of FIG. 17 illustrates an undershoot condition wherethe subject initially undershoots the second position (P2) of the targetwith his or her eyes (e.g., the subject undershoots the target by 50%).

While the eye movement and/or eye position of the subject is beingdetermined in conjunction with the postural sway of the subject in thetesting procedure described above, the subject may be instructed toperform a variety of different vestibular or ocular motor tests. Inparticular, the subject may be instructed to perform any one or more ofthe following vestibular or ocular motor tests: (i) a test involvingsmooth pursuits, (ii) a test involving saccades, (iii) a near pointconvergence (NPC) test, (iv) a vestibular-ocular reflex (VOR) test, and(v) a visual motion sensitivity (VMS) test. Each of these variousvestibular or ocular motor tests will be explained below.

A smooth pursuits test evaluates the ability of a subject's eye tofollow a slowly moving target. During this test, the subject and theclinician may be seated, or the clinician may be standing while thesubject is also standing. During this test, the clinician holds anobject (e.g., his or her fingertip) a predetermined distance from thesubject (e.g., a distance between two and four feet). The subject isinstructed by the clinician to maintain focus on the object as theclinician horizontally displaces the object in a smooth manner apredetermined distance to the left and to the right of a centerline(e.g., two feet to the right of the centerline and two feet to the leftof the centerline). During a single repetition, the object is moved backand forth to the starting position. A predetermined number of horizontaldisplacement repetitions may be performed during the smooth pursuitstest (e.g., a total of three horizontal displacement repetitions).During the performance of the test, the object may be displaced atpredetermined rate (e.g., the object may be displaced at predeterminedrate such that it takes approximately 1.5 to 2.5 seconds to go fullyfrom the left to the right and approximately 1.5 to 2.5 seconds to gofully from the right to the left). Then, during the second part of thetest, the subject is instructed again by the clinician to maintain focuson the object as the clinician vertically displaces the object in asmooth manner a predetermined distance above and below a centerline(e.g., two feet above and below the centerline). As for the horizontaldisplacement portion of the test described above, a predetermined numberof vertical displacement repetitions may be performed during the smoothpursuits test (e.g., a total of three vertical displacementrepetitions). Also, as explained above for the horizontal displacementportion of the test, the object may be displaced at predetermined rate(e.g., the object may be displaced at predetermined rate such that ittakes approximately 1.5 to 2.5 seconds to go fully from the lowestdownward position to the highest upward position and approximately 1.5to 2.5 seconds to go fully from the highest upward position to thelowest downward position). In addition, during the performance of thesmooth pursuits test, the following symptoms of the subject may betracked and recorded by the clinician: (i) headache, (ii) dizziness,(iii) fogginess, and (iv) nausea.

A saccades test evaluates the ability of a subject's eyes to movequickly between targets. During this test, the subject and the clinicianmay be seated, or the clinician may be standing while the subject isalso standing. During horizontal saccades, the clinician holds twohorizontally spaced-apart objects (e.g., his or her fingertips) apredetermined distance from the subject (e.g., a distance between twoand four feet). Each of the first and second objects is spaced apredetermined horizontal distance from an imaginary centerline betweenthe objects (e.g., two feet to the right of the centerline and two feetto the left of the centerline) so that a predetermined gaze range forthe subject is established (e.g., 35 degrees to the left and 35 degreesto the right). During the test, the subject is instructed by theclinician to move his or eyes quickly back and forth from the firstobject to the second object. During a single repetition, the eyes of thesubject are moved back and forth to the starting position. Apredetermined number of repetitions may be performed during thehorizontal saccades test (e.g., a total of ten repetitions). During theperformance of the horizontal saccades test, the following symptoms ofthe subject may be tracked and recorded by the clinician: (i) headache,(ii) dizziness, (iii) fogginess, and (iv) nausea. During verticalsaccades, the clinician holds two vertically spaced-apart objects (e.g.,his or her fingertips) a predetermined distance from the subject (e.g.,a distance between two and four feet). Each of the first and secondobjects is spaced a predetermined vertical distance from an imaginarycenterline between the objects (e.g., two feet above the centerline andtwo feet below the centerline) so that a predetermined gaze range forthe subject is established (e.g., 35 degrees upward and 35 degreesdownward). During the test, the subject is instructed by the clinicianto move his or eyes quickly up and down from the first object to thesecond object. During a single repetition, the eyes of the subject aremoved up and down to the starting position. A predetermined number ofrepetitions may be performed during the vertical saccades test (e.g., atotal of ten repetitions). During the performance of the verticalsaccades test, the following symptoms of the subject may be tracked andrecorded by the clinician: (i) headache, (ii) dizziness, (iii)fogginess, and (iv) nausea.

A near point convergence (NPC) test evaluates the ability of a subject'seyes to view a near target without convergence. During this test, thesubject may be standing on the force measurement assembly 102 andwearing his or her corrective lenses, if necessary. The clinician may bestanding in front of the subject so that he or she may observe thesubject's eye movement during the performance of the test. During theperformance of the NPC test, the subject focuses on a small target(e.g., a letter that has approximately 0.2 to 0.25 inches in height)that is spaced approximately an arm's length distance away from the faceof the subject. As the NPC test is performed, the subject slowlydisplaces the small target towards the tip of his or her nose. Thesubject is instructed to stop displacing the target towards his or hernose when he or she sees two distinct images or the clinician observesan outward deviation of one eye. During the test, the subject isinstructed to ignore the blurring of the image. Once the subject hasstopped displacing the target towards his or her nose, the distancebetween the target and the tip of the nose of the subject is measuredand recorded. A predetermined number of repetitions of the NPC test maybe performed (e.g., a total of three or four repetitions). The measureddistance is recorded during each of the repetitions. During theperformance of the NPC test, the following symptoms of the subject maybe tracked and recorded by the clinician: (i) headache, (ii) dizziness,(iii) fogginess, and (iv) nausea. An abnormal near point of convergenceis considered to be greater than or equal to 6 centimeters from the tipof the nose.

A vestibular-ocular reflex (VOR) test evaluates the subject's ability tostabilize vision as the head moves. During this test, the subject may bestanding on the force measurement assembly 102. The clinician may bestanding in front of the subject so that he or she may observe thesubject's eye movement during the performance of the test. During theperformance of the VOR test, the subject focuses on a small target(e.g., a letter that has approximately 0.2 to 0.25 inches in height)that is spaced a predetermined distance away from the face of thesubject (e.g., a predetermined distance of between two (2) feet and four(4) feet). At the beginning of the VOR test, the clinician holds thesmall target at a centerline position in front of the subject. Duringthe horizontal VOR test, the subject is instructed to rotate their headhorizontally while maintaining focus on the target. In particular, thesubject may be instructed to rotate his or her head at a predeterminedamplitude (e.g., 20 to 30 degrees) to each side, and a metronome may beused to ensure that the speed of rotation is maintained at apredetermined number of beats per minute (e.g., 180 to 200 beats perminute and/or one beat in each direction). During a single repetition,the head of the subject is moved back and forth to the startingposition. A predetermined number of repetitions may be performed duringthe horizontal VOR test (e.g., a total of ten repetitions). During theperformance of the horizontal VOR test, the following symptoms of thesubject may be tracked and recorded by the clinician: (i) headache, (ii)dizziness, (iii) fogginess, and (iv) nausea. During the vertical VORtest, the subject displaces his or her head vertically, rather thanhorizontally. In particular, during the vertical VOR test, the subjectmay be instructed to rotate his or her head at a predetermined amplitude(e.g., 20 to 30 degrees) up and down, and a metronome may be used toensure that the speed of rotation is maintained at a predeterminednumber of beats per minute (e.g., 180 to 200 beats per minute and/or onebeat in each direction). During a single repetition, the head of thesubject is moved up and down to the starting position. A predeterminednumber of repetitions may be performed during the vertical VOR test(e.g., a total of ten repetitions). During the performance of thevertical VOR test, the following symptoms of the subject may be trackedand recorded by the clinician: (i) headache, (ii) dizziness, (iii)fogginess, and (iv) nausea.

A visual motion sensitivity (VMS) test evaluates the subject's visualmotion sensitivity and the ability to inhibit vestibular-induced eyemovements using vision. During this test, the subject may be standing onthe force measurement assembly 102 with his or her feet spread apart.The clinician may stand next to and slightly behind the subject, so thatthe subject is guarded but the subject is able to freely perform themovements during the test. During the test, the subject may hold atleast one of his or her arms outstretched while focusing on his or herthumb. Maintaining focus on his or her thumb, the subject rotates,together as a generally single unit, his or her head, eyes, and trunk ata predetermined amplitude to the right and to the left (e.g., at anamplitude between 60 degrees and 80 degrees to the right and to theleft). During the performance of the VMS test, a metronome may be usedto ensure that the speed of rotation is maintained at a predeterminednumber of beats per minute (e.g., 50 beats per minutes and/or one beatin each direction). A single repetition is complete when the trunkrotates back and forth to the standing position. A predetermined numberof repetitions may be performed during the vertical VMS test (e.g., atotal of five repetitions). During the performance of the VMS test, thefollowing symptoms of the subject may be tracked and recorded by theclinician: (i) headache, (ii) dizziness, (iii) fogginess, and (iv)nausea.

In one or more embodiments, the tests performed on the subject 108 maybe designed to induce symptoms from the subject 108 (i.e. to push thesubject 108 into having particular symptoms, such as those listed in thepreceding paragraph) so that the clinician may determine which symptomsbecome worse during the testing. Also, in these one or more embodiments,while the tests are performed on the subject 108, the induced symptomsmay be tracked by the clinician.

One alternative embodiment of the system for measuring postural sway,eye movement and/or eye position, and gaze direction is seen generallyat 100″ in FIG. 20. The system of FIG. 20 is similar in most respects tothe system of FIG. 1. However, rather than using a postural swaydetection device in the form of the force plate 102 as in FIG. 1, thesystem of FIG. 20 includes a postural sway detection device in the formof a plurality of inertial measurement units 212 (IMUs 212). As shown inFIG. 20, the subject or patient 108 may be outfitted with a plurality ofdifferent inertial measurement units 212 for determining the motion andpostural sway of the subject. In the illustrative embodiment, thesubject 108 is provided with two (2) inertial measurement units 212 oneach of his legs 108 a, 108 b (e.g., on the side of his legs 108 a, 108b). The subject is also provided with two (2) inertial measurement units212 on each of his arms 108 c, 108 d (e.g., on the side of his arms 108c, 108 d). In addition, the subject 108 of FIG. 20 is provided with aninertial measurement unit 212 around his waist (e.g., with the IMUlocated on the back side of the subject 108), and another inertialmeasurement unit 212 around his or her chest (e.g., with the IMU locatedon the front side of the subject 108 near his sternum). In theillustrated embodiment, each of the inertial measurement units 212 isoperatively coupled to the data acquisition/data processing device 104by wireless means, such as Bluetooth, or another suitable type ofpersonal area network wireless means. Additional details of the IMUhardware and the calculation procedures performed in conjunction withthe inertial measurement units 212 will be described hereinafter.

In the illustrated embodiment of FIG. 20, each of the inertialmeasurement units 212 is coupled to the respective body portion of thesubject 108 by a band 210. As shown in FIG. 20, each of the inertialmeasurement units 212 comprises an IMU housing attached to an elasticband 210. The band 210 is resilient so that it is capable of beingstretched while being placed on the subject 108 (e.g., to accommodatethe hand or the foot of the subject 108 before it is fitted in place onthe arm 108 c, 108 d or the leg 108 a, 108 b of the subject 108). Theband 210 can be formed from any suitable stretchable fabric, such asneoprene, spandex, and elastane. Alternatively, the band 210 could beformed from a generally non-stretchable fabric, and be provided withlatching means or clasp means for allowing the band 210 to be split intotwo portions (e.g., the band 210 could be provided with a snap-typelatching device).

In other embodiments, it is possible to attach the inertial measurementunits 212 to the body portions of the subject 108 using other suitableattachment means. For example, the inertial measurement units 212 may beattached to a surface (e.g., the skin or clothing item of the subject108) using adhesive backing means. The adhesive backing means maycomprise a removable backing member that is removed just prior to theinertial measurement unit 212 being attached to a subject 108 or object.Also, in some embodiments, the adhesive backing means may comprise aform of double-sided bonding tape that is capable of securely attachingthe inertial measurement unit 212 to the subject 108 or another object.

Another alternative embodiment of the system for measuring posturalsway, eye movement and/or eye position, and gaze direction is seengenerally at 100′″ in FIG. 21. The system of FIG. 21 is similar in mostrespects to the systems of FIGS. 1 and 20. However, rather than using apostural sway detection device in the form of the force plate 102 as inthe system of FIG. 1, or a postural sway detection device comprising aplurality of inertial measurement units 212 as in the system of FIG. 20,the system of FIG. 21 includes a postural sway detection device in theform of a plurality of optical motion capture devices (i.e., videocameras 214) that capture the motion of the subject so that the posturalsway of the subject 108 may be determined therefrom. The video cameras214 of the optical motion capture system generate motion capture datarepresentative of the captured motion (i.e., video images) of thesubject 108. While three (3) cameras 214 are depicted in FIG. 21, one ofordinary skill in the art will appreciate that more or less cameras canbe utilized, provided that at least two cameras 214 are used.

The motion capture system illustrated in FIG. 21 is a markerless-typemotion detection/motion capture system. That is, the motion capturesystem of FIG. 21 uses a plurality of high speed video cameras to recordthe motion of a subject without requiring any markers to be placed onthe subject. However, in another embodiment, a marker-based motioncapture system is utilized. In this embodiment, the subject is providedwith a plurality of markers disposed thereon. These markers are used torecord the position of the limbs of the subject in 3-dimensional space.In this embodiment, the plurality of cameras 214 are used to track theposition of the markers as the subject moves his or her limbs in3-dimensional space. For example, the subject may have a plurality ofsingle markers applied to anatomical landmarks (e.g., the iliac spinesof the pelvis, the malleoli of the ankle, and the condyles of the knee),or clusters of markers applied to the middle of body segments. As thesubject executes particular movements, the data acquisition/dataprocessing device 104 calculates the trajectory of each marker in three(3) dimensions. Then, once the positional data is obtained using themotion capture system, the position of the subject's torso and limbs maybe determined, and inverse kinematics may be employed in order todetermine the joint angles of the subject. Both of the aforementionedmarkerless and marker-based motion capture systems are optical-basedsystems. It is also to be understood that, rather than using an opticalmotion detection/capture system, a suitable magnetic orelectro-mechanical motion detection/capture system can also be employedin the system 100′″ described herein.

Yet another alternative embodiment of the system for measuring posturalsway, eye movement and/or eye position, and gaze direction is seengenerally at 100″″ in FIG. 22. The system of FIG. 22 is similar in mostrespects to the systems of FIGS. 1, 20, and 21. However, rather thanusing a postural sway detection device in the form of the force plate102 as in the system of FIG. 1, a postural sway detection devicecomprising a plurality of inertial measurement units 212 as in thesystem of FIG. 20, or postural sway detection device comprising aplurality of optical motion capture devices 214 as in the system of FIG.21, the system of FIG. 22 includes a postural sway detection device inthe form of a motion capture device 216 that employs infrared light tocapture the motion of the subject 108 (e.g., the device 216 of FIG. 22utilizes an infrared (IR) emitter to project a plurality of dots ontoobjects in a particular space as part of a markless motion capturesystem). As shown in FIG. 22, a motion capture device 216 with one ormore cameras 218, one or more infrared (IR) depth sensors 220, and oneor more microphones 222 may be used to provide full-bodythree-dimensional (3D) motion capture, facial recognition, and voicerecognition capabilities. In FIG. 22, it can be seen that the motioncapture device 216 may be supported on the wall of the space by means ofa shelf 224.

In one or more other embodiments, a method for determining a gazedirection of a subject during a balance test and/or concussion screeningtest is performed using the system illustrated in FIG. 1. Initially, theeye movement tracking device 124 is positioned on the subject 108 or onan object proximate to the subject 108. In FIG. 1, it can be seen thatthe eye movement tracking device 124 is in the form of goggles orglasses worn on the head of the subject 108. In addition, the headposition detection device 122 is also positioned on the head of thesubject 108 or on an object proximate to the head of the subject 108. Inthe illustrated embodiment of FIG. 1, it can be seen that the headposition detection device 122 is integrated into the goggles containingthe eye movement tracking device 124 (e.g., the head position detectiondevice 122 may be in the form of an inertial measurement unit (IMU)integrated in the goggles worn by the subject 108). Also, during theperformance of the method, at least one limb position detection device128 is positioned on one or more limbs of the subject 108. For example,in the illustrative embodiment of FIG. 1, an inertial measurement unit(IMU) may be attached to one or both arms of the subject 108. Once thesubject has been outfitted with the measurement devices 122, 124, 128,the eye movement and/or eye position of the subject 108 is measuredusing the eye movement tracking device 124 and the head position of thesubject 108 is measured using the head position detection device 122while at least one of the one or more limbs of the subject 108 and thehead of the subject 108 are displaced by the subject 108. In theillustrated embodiment, the head position detection device 122 and theeye movement tracking device 124 may each be operatively coupled to thedata acquisition/data processing device 104 by wireless means, such asBluetooth, or another suitable type of personal area network wirelessmeans.

In one or more embodiments, each inertial measurement unit (e.g., eachinertial measurement units 212) may comprise a triaxial (three-axis)accelerometer sensing linear acceleration d′, a triaxial (three-axis)rate gyroscope sensing angular velocity {right arrow over (ω)}′, atriaxial (three-axis) magnetometer sensing the magnetic north vector{right arrow over (n)}′, and a central control unit or microprocessoroperatively coupled to each of accelerometer, gyroscope, and themagnetometer. In addition, each inertial measurement unit may comprise awireless data interface for electrically coupling the inertialmeasurement unit to the data acquisition/data processing device 104.

Next, an illustrative manner in which the data acquisition/dataprocessing device 104 of the system 100 in FIG. 1 performs the inertialmeasurement unit (IMU) calculations will be explained in detail (e.g.,for each inertial measurement unit 212). In particular, this calculationprocedure will describe the manner in which the orientation and positionof one or more body portions (e.g., arms and head) of a subject 108could be determined using the signals from the plurality of inertialmeasurement units (IMUs) of the system 100. As explained above, in oneor more embodiments, each inertial measurement unit includes thefollowing three triaxial sensor devices: (i) a three-axis accelerometersensing linear acceleration {right arrow over (d)}′, (ii) a three-axisrate gyroscope sensing angular velocity {right arrow over (ω)}′, and(iii) a three-axis magnetometer sensing the magnetic north vector {rightarrow over (n)}′. Each inertial measurement unit senses in the local(primed) frame of reference attached to the IMU itself. Because each ofthe sensor devices in each IMU is triaxial, the vectors {right arrowover (a)}′, {right arrow over (w)}′, {right arrow over (n)}′ are each3-component vectors. A prime symbol is used in conjunction with each ofthese vectors to symbolize that the measurements are taken in accordancewith the local reference frame. The unprimed vectors that will bedescribed hereinafter are in the global reference frame.

The objective of these calculations is to find the orientation θ(t) andposition {right arrow over (R)}(t) in the global, unprimed, inertialframe of reference. Initially, the calculation procedure begins with aknown initial orientation {right arrow over (θ)}₀ and position {rightarrow over (R)}₀ in the global frame of reference.

For the purposes of the calculation procedure, a right-handed coordinatesystem is assumed for both global and local frames of reference. Theglobal frame of reference is attached to the Earth. The acceleration dueto gravity is assumed to be a constant vector {right arrow over (g)}.Also, for the purposes of the calculations presented herein, it ispresumed the sensor devices of the inertial measurement units (IMUs)provide calibrated data. In addition, all of the signals from the IMUsare treated as continuous functions of time. Although, it is to beunderstood the general form of the equations described herein may bereadily discretized to account for IMU sensor devices that take discretetime samples from a bandwidth-limited continuous signal.

The orientation {right arrow over (θ)}(t) is obtained by singleintegration of the angular velocity as follows:

$\begin{matrix}{{\overset{\rightarrow}{\theta}(t)} = {{\overset{\rightarrow}{\theta}}_{0} + {\int_{0}^{t}{{\overset{\overset{->}{\_}}{\omega}(t)}{dt}}}}} & (17) \\{{\overset{\rightarrow}{\theta}(t)} = {{\overset{\rightarrow}{\theta}}_{0} + {\int_{0}^{t}{{\overset{\rightarrow}{\Theta}(t)}{{\overset{\overset{->}{\_}}{\omega}}^{\prime}(t)}{dt}}}}} & (18)\end{matrix}$where {right arrow over (Θ)}(t) is the matrix of the rotationtransformation that rotates the instantaneous local frame of referenceinto the global frame of reference.

The position is obtained by double integration of the linearacceleration in the global reference frame. The triaxial accelerometerof each IMU senses the acceleration {right arrow over (a)}′ in the localreference frame. The acceleration {right arrow over (a)}′ has thefollowing contributors: (i) the acceleration due to translationalmotion, (ii) the acceleration of gravity, and (iii) the centrifugal,Coriolis and Euler acceleration due to rotational motion. All but thefirst contributor has to be removed as a part of the change of referenceframes. The centrifugal and Euler accelerations are zero when theacceleration measurements are taken at the origin of the local referenceframe. The first integration gives the linear velocity as follows:

$\begin{matrix}{{\overset{->}{v}(t)} = {{\overset{->}{v}}_{0} + {\int_{0}^{t}{\left\{ {{\overset{->}{a}(t)} - \overset{\rightarrow}{g}} \right\}{dt}}}}} & (19) \\{{\overset{->}{v}(t)} = {{\overset{->}{v}}_{0} + {\int_{0}^{t}{\left\{ {{{\overset{\rightarrow}{\Theta}(t)}\left\lbrack {{{\overset{\rightarrow}{a}}^{\prime}(t)} + {2\overset{->}{\omega} \times {{\overset{->}{v}}^{\prime}(t)}}} \right\rbrack} - \overset{->}{g}} \right\}{dt}}}}} & (20)\end{matrix}$where 2{right arrow over (ω)}′×{right arrow over (ν)}′(t) is theCoriolis term, and where the local linear velocity is given by thefollowing equation:{right arrow over (v)}′(t)={right arrow over (Θ)}^(−I)(t){right arrowover (ν)}(t)  (21)The initial velocity {right arrow over (v)}₀ can be taken to be zero ifthe motion is being measured for short periods of time in relation tothe duration of Earth's rotation. The second integration gives theposition as follows:

$\begin{matrix}{{\overset{\rightarrow}{R}(t)} = {{\overset{->}{R}}_{0} + {\int_{0}^{t}{{\overset{->}{v}(t)}dt}}}} & (22)\end{matrix}$At the initial position, the IMU's local-to-global rotation's matrix hasan initial value {right arrow over (Θ)}(0)≡{right arrow over (Θ)}₀. Thisvalue can be derived by knowing the local and global values of both themagnetic north vector and the acceleration of gravity. Those two vectorsare usually non-parallel. This is the requirement for the {right arrowover (Θ)}₀({right arrow over (g)}′, {right arrow over (n)}′, {rightarrow over (g)}, {right arrow over (n)}) to be unique. The knowledge ofeither of those vectors in isolation gives a family of non-uniquesolutions {right arrow over (Θ)}₀({right arrow over (g)}′, {right arrowover (g)}) or {right arrow over (Θ)}₀({right arrow over (n)}′, {rightarrow over (n)}) that are unconstrained in one component of rotation.The {right arrow over (Θ)}₀({right arrow over (g)}′, {right arrow over(n)}′, {right arrow over (g)}, {right arrow over (n)}) has manyimplementations, with the common one being the Kabsch algorithm. Assuch, using the calculation procedure described above, the dataacquisition/data processing device 104 of the system 100 may determinethe orientation {right arrow over (θ)}(t) and position {right arrow over(R)}(t) of one or more body portions of the subject 108. For example,the orientation of one or more limbs of the subject 108 (e.g., theorientation of the arms of the subject 108 in FIG. 1) may be determinedby computing the orientation {right arrow over (θ)}(t) and position{right arrow over (R)}(t) of two points on the limb of the subject 108(i.e., at the respective locations of two inertial measurement units(IMUs) disposed on the limb of the subject 108).

In the system of FIG. 20, where the postural sway detection device is inthe form of one or more inertial measurement units 212 (IMUs 212), thecenter of gravity (COG) for the subject 108 may be determined by thedata acquisition/data processing device 104 using the position of thetorso determined from the one or more inertial measurement units 212attached to the torso of the subject 108 (i.e., computed using theequation (22) above). For example, the height of the subject 108 may beentered into the data acquisition/data processing device 104 by theclinician, and then using the entered height of the subject 108, thecenter of gravity (COG) of the subject 108 may be estimated to be apredetermined distance (e.g., a specified number of inches) from one ofthe inertial measurement units 212 attached to the torso of the subject108. Also, if the subject 108 is presumed to bend only at his or herankles, the subject 108 may be modeled as an inverted pendulum by thedata acquisition/data processing device 104, thus permitting thepostural sway displacement and/or the postural sway angle for thesubject 108 to be determined by the data acquisition/data processingdevice 104 based upon the positional output data from one or more of theinertial measurement units 212 in FIG. 20. For example, the average ofthe sway displacement of the subject 108 may be presumed to be theupright zero sway position of subject 108, and then the deviations fromthe zero sway position of the subject 108 determined by the positionaloutput data from the inertial measurement units 212 may be used todetermine the postural sway displacement and/or the postural sway angle.

In a further embodiment, rather than providing a postural sway detectiondevice in the form of a plurality of inertial measurement units 212(IMUs 212) attached to different portions of the body of the subject 108(as shown in FIG. 20), the postural sway detection device may be in theform of one or more inertial measurement units attached only to the headof the subject 108. In this further embodiment, the center of gravity(COG) for the subject 108 may be determined by the data acquisition/dataprocessing device 104 using the position of the head determined from theone or more inertial measurement units attached to the head of thesubject 108 (i.e., computed using the equation (22) above). For example,as explained above, the height of the subject 108 may be entered intothe data acquisition/data processing device 104 by the clinician, andthen using the entered height of the subject 108, the center of gravity(COG) of the subject 108 may be estimated to be a predetermined distance(e.g., a specified number of inches) from one or more inertialmeasurement units attached to the head of the subject 108. Also, if thesubject 108 is presumed to bend only at his or her ankles, the subject108 may be modeled as an inverted pendulum by the data acquisition/dataprocessing device 104, thus permitting the postural sway displacementand/or the postural sway angle for the subject 108 to be determined bythe data acquisition/data processing device 104 based upon thepositional output data from the one or more inertial measurement unitsattached to the head of the subject 108. For example, the average of thesway displacement of the subject 108 may be presumed to be the uprightzero sway position of subject 108, and then the deviations from the zerosway position of the subject 108 determined by the positional outputdata from the one or more head-mounted inertial measurement units may beused to determine the postural sway displacement and/or the posturalsway angle.

In an alternative embodiment, rather than the eye movement trackingdevice 124 being integrated into goggles or glasses worn on the head ofthe subject 108, the eye movement tracking device may be in the form ofan eye movement tracking device 226 disposed on a graspable object(e.g., an elongate member 230, such as a stick—refer to the system100′″″ of FIG. 23) held in the hands of the subject 108 during theperformance of the balance test and/or the concussion screening test. Inthis alternative embodiment, the eye movement tracking device 226 (e.g.,a video camera) may capture the movement and/or position of thesubject's eyes while he or she performs the balance test and/or theconcussion screening test. Also, as shown in FIG. 23, the eye movementtracking device 226 may comprise a light emitting diode 228 (i.e., anLED 228) disposed thereon so as to provide a target for the subject 108(i.e., the subject 108 maintains his or her gaze on the LED 228 duringthe performance of a test). In this alternative embodiment, the headposition detection device 122′ is still disposed on the head of thesubject 108. For example, as shown in the illustrated embodiment of FIG.23, the head position detection device 122′ comprises an inertialmeasurement unit (IMU) that is attached to the head of the subject 108via a headband 123.

In one or more alternative embodiments, rather than being in the form ofan inertial measurement unit (IMU), the head position detection devicemay be in the form of a video camera, an infrared sensor, or anultrasonic sensor. In these one or more alternative embodiments, thehead position of the subject 108 is measured using the video camera, theinfrared sensor, or the ultrasonic sensor so that the gaze direction maybe determined.

For example, in the illustrated embodiment of FIG. 1, the eye movement,the eye position, and the head position of the subject 108 are eachsimultaneously measured while the arms and torso or trunk of the subject108 are rotated together in a side-to-side manner, and the head of thesubject 108 is rotated generally in sync with the arms and trunk of thesubject 108. In the illustrative embodiment of FIG. 1, the arms of thesubject 108 may be extended outwardly from the torso or trunk of thesubject 108 in a generally perpendicular manner from the subject's trunkor torso. When the arms of the subject 108 are extended outwardly fromthe torso or trunk of the subject 108, the subject 108 may clasp his orher hands together with his or her thumbs pointing generally upwardlyfrom his or her hands. During the simultaneous rotation of the head ofthe subject 108 and the arms of the subject 108, the subject 108 triesto continually maintain his or her gaze orientation on a portion of hisor her hands during arm rotation (e.g., the subject 108 tries tomaintain his or her visual focus on his or her upwardly pointed thumbs).In an exemplary embodiment, the subject 108 may be instructed todisplace his or her head and arms over a prescribed angular range (e.g.,plus or minus 40 degrees or plus or minus 30 degrees). The actualangular range traversed by the subject 108 may be verified by the headposition detection device 122 (e.g., IMU) that is disposed on the headof the subject 108. That is, the head position detection device 122 mayoutput an angular range (e.g., plus or minus 35 degrees) that isachieved during the subject's rotation of his or her head.Alternatively, rather than using the head position detection device 122disposed on the head of the subject 108, the angular range of movementachieved by the head of the subject 108 may be determined using a visualindicator device (e.g., a light 232) attached to the head of the subject108 (see FIG. 1). In this alternative embodiment, a projection of thelight beam emitted by the light 232 onto a surface disposed in front ofthe subject 108 (e.g., a wall) may be used to approximate the angularrange of movement achieved by the subject 108. For example, the path ofthe light beam may be compared to spaced-apart markers 234, 236, 238disposed on the surface in front of the subject 108 (e.g., the wall) todetermine if approximately the correct range of angular movement isbeing achieved by the subject. In FIG. 1, the first marker 234 on theleft side indicates the minus 30 degree position, the second marker 236in the center indicates the zero degree position, and the third marker238 on the right side indicates the 35 degree position.

In an alternative embodiment, rather than using the head positiondetection device 122 or the light 232 on the head of the subject 108,the head position of the subject 108 may be alternatively displayed on avisual display device 250 (refer to the system 100″″″ of FIG. 24). Inthe system 100″″″ of FIG. 24, the subject 108 may be outfitted with apointer device 248 on his head, which controls the positon of a cursor246 on the output screen of the visual display device 250. In thisembodiment, the pointer device 248 and the visual display device 250 areoperatively coupled to the data processing device 104 such that thepositon of the cursor 246 on the visual display device 250 is controlledbased upon the output of the pointer device 248. For example, thepointer device 248 may be wirelessly coupled to the data processingdevice 104, and the visual display device 250 may be coupled to the dataprocessing device 104 by data transmission cable 120. As such, thecursor 246 on the visual display device 250 is indicative of the headposition of the subject 108. Referring again to FIG. 24, it can be seenthat the image displayed on the output screen of the visual displaydevice 250 further comprises spaced-apart markers 240, 242, 244 that areused to determine if the correct range of angular movement is beingachieved by the subject. In FIG. 24, the first marker 240 on the leftside indicates the minus 30 degree position, the second marker 242 inthe center indicates the zero degree position, and the third marker 244on the right side indicates the 30 degree position. Thus, during therotation of his head, subject 108 tries to displace the cursor 246back-and-forth between the vertical markers 240, 244 on the outputscreen of the visual display device 250. Advantageously, the use of thepointer device 248 and the visual display device 250 for determining thehead position of the subject 108 enables the angular range of headdisplacement to be easily modified by simply adjusting the locations ofthe vertical markers 240, 244 on the output screen of the visual displaydevice 250.

Referring to FIGS. 19A-19D, exemplary output results are presented for abalance test and/or the concussion screening test where the subject 108is simultaneously rotating his or her arms, torso, and head generally insync with one another (i.e., a test where the subject's head, torso, andoutwardly extended arms are generally being displaced in sync with oneanother). Initially, referring to FIG. 19A, the sinusoidal curve 202represents the angular position of the subject's head (θ_(H)) over time(the sinusoidal curve 202 is indicative of the oscillatory motion of thesubject's head where the subject's head is rotated back and forth withinan angular range, e.g., −30 degrees to 30 degrees). Then, as shown inFIG. 19B, the curve 204 represents the angular position of the subject'seye (θ_(E)) over time (because the head of the subject 108 is generallybeing rotated with the target, the eyes of the subject 108 do notgenerally move with respect to the head of the subject 108, as depictedby the curve 204 in FIG. 19B, which is nearly equal to zero over time).Next, as shown in FIG. 19C, because the gaze direction is generallyequal to the sum of the head movement and the eye position, and theangular position of the subject's eye (θ_(E)) is nearly equal to zeroduring the test, the angular position of the subject's gaze (θ_(G)) isapproximately equal to the angular position of the subject's head(θ_(H)) during the test (as illustrated by the sinusoidal curve 206 inFIG. 19C, which is almost equal to the head angular position curve 202in FIG. 19A). Finally, as depicted in FIG. 19D, the sinusoidal curve 208represents the angular position of the target (θ_(T)) over time (thesinusoidal curve 208 is indicative of the oscillatory motion of thetarget where the target is rotated back and forth within an angularrange, e.g., −30 degrees to 30 degrees) during the balance test and/orthe concussion screening test.

In an alternative embodiment, rather than the subject 108 simultaneouslyrotating his or her arms, torso, and head in sync with one anotherduring the performance of the balance test and/or the concussionscreening test, the subject 108 may rotate his or her head, while thearms of the subject 108 are extended outwardly and stationary, and whilea gaze orientation of the subject 108 is maintained on the upwardlypointing thumbs of the hands of the subject's outwardly extending arms.As in the illustrative embodiment described above, the eye movement, theeye position, and the head position of the subject 108 aresimultaneously measured while the subject 108 performs the test inaccordance with this alternative embodiment (i.e., head rotated, armsstationary, and subject's gaze fixed on the thumbs of the hands).

Referring to FIGS. 18A-18D, exemplary output results are presented for atest where the subject 108 is rotating his or head, while the arms ofthe subject 108 are extended outwardly and stationary, and while a gazeorientation of the subject 108 is maintained on the upwardly pointingthumbs of the hands of the subject's outwardly extending arms (i.e., atest where the subject's head is moving without the subject's torso andtarget moving). Initially, referring to FIG. 18A, the sinusoidal curve188 represents the angular position of the subject's head (θ_(H)) overtime (the sinusoidal curve 188 is indicative of the oscillatory motionof the subject's head where the subject's head is rotated back and forthwithin an angular range, e.g., −30 degrees to 30 degrees). Then, asshown in FIG. 18B, the sinusoidal curve 190 represents the angularposition of the subject's eye (θ_(E)) over time (the sinusoidal curve190 is indicative of the oscillatory motion of the subject's eye wherethe subject's eye is rotated back and forth in a direction that isgenerally equal and opposite to the motion of the subject's head so thatthe subject 108 is able to maintain his or her gaze fixed on thestationary target). In other words, the sinusoidal curve 190 in FIG. 18Brepresents the subject's eye movement with respect to his or her head.Next, as shown in FIG. 18C, because the gaze direction is generallyequal to the sum of the head movement and the eye position, and theangular position of the subject's eye (θ_(E)) is generally equal andopposite to the movement of the subject's head in the illustrativeexample of FIGS. 18A-18D, the angular position of the subject's gaze(θ_(G)) is approximately equal to zero (as illustrated by the curve 192in FIG. 18C). Finally, as depicted in FIG. 18D, because the target issubstantially stationary in the illustrative example of FIGS. 18A-18D,the angular position of the target (θ_(T)) is generally equal to zero(as illustrated by the curve 194 in FIG. 18D).

Also, in an alternative embodiment, rather than performing a visualmotion sensitivity-type test wherein the arms, torso, and head of thesubject 108 are rotated in sync with one another, the subject mayalternatively perform one of the other types of vestibular or ocularmotor tests described above in conjunction with the balance test and/orthe concussion screening test. In particular, during the balance and/orthe concussion screening test, the subject may be instructed to performany one or more of the following other vestibular or ocular motor testsexplained above: (i) a test involving smooth pursuits, (ii) a testinvolving saccades, (iii) a near point convergence (NPC) test, and (iv)a vestibular-ocular reflex (VOR) test.

During the abovedescribed rotation of at least one of the one or morelimbs of the subject 108 and the head of the subject 108, the eyemovement tracking device 124 outputs one or more first signals that arerepresentative of the detected eye movement and/or eye position of thesubject 108 to the data acquisition/data processing device 104, and thehead position detection device 122 outputs one or more second signalsthat are representative of the detected position of the head of thesubject 108 to the data acquisition/data processing device 104. Afterwhich, the data acquisition/data processing device 104 is speciallyprogrammed to determine one or more gaze directions of the subject 108from the one or more first signals output by the eye movement trackingdevice 124 and the one or more second signals output by the headposition detection device 122. The data acquisition/data processingdevice 104 also is specially programmed to determine a position of oneor more limbs of the subject 108 from the one or more third signalsoutput by the at least one limb position detection device 128. Inaddition, the data acquisition/data processing device 104 is furtherspecially programmed to determine whether the one or more gazedirections of the subject 108 that are determined from the one or morefirst signals and the one or more second signals correspond to adirection in which the one or limbs of the subject 108 are pointed whilethe at least one of the one or more limbs of the subject 108 and thehead of the subject 108 are displaced by the subject 108 during theperformance of the balance test and/or the concussion screening test.

Also, in the illustrative embodiment of FIG. 1, it can be seen that thesubject 108 is further positioned in an upright position on a forcemeasurement assembly (i.e., the force plate 102) while the at least oneof the one or more limbs of the subject 108 and the head of the subject108 are displaced by the subject 108 during the performance of thebalance test and/or the concussion screening test. In particular, theforce plate 102 may be used to determine the postural sway of thesubject 108 during the performance of the balance test and/or theconcussion screening test. That is, the force measurement assembly 102outputs one or more fourth signals representative of forces and/ormoments being applied to the surface 114, 116 of the force measurementassembly 102 by the subject while at least one of the one or more limbsof the subject 108 and the head of the subject 108 are displaced by thesubject 108. The data acquisition/data processing device 104 isspecially programmed to convert the one or more fourth signals that arerepresentative of the forces and/or moments applied to the surface 114,116 of the force measurement assembly 102 by the subject into one ormore load output values (a combination of force and moments, asdescribed above). After which, the data acquisition/data processingdevice 104 is specially programmed to compute one or more numericalvalues (e.g., one or more postural sway angles) that are indicative of apostural stability of the subject 108 by using the one or more loadoutput values (i.e., the computed forces and moments) while at least oneof the one or more limbs of the subject 108 and the head of the subject108 are displaced by the subject 108.

In one or more embodiments, during the performance of the balance testand/or the concussion screening test described above, the dataacquisition/data processing device 104 is specially programmed togenerate an audio output signal that corresponds to the proper limband/or head rotation timing of the subject 108, and to output that audiooutput signal to speakers of the data acquisition/data processing device104 in order to assist the subject 108 with the proper limb and/or headrotation timing that is required for the balance test and/or theconcussion screening test (i.e., a metronome plays from the speakers ofthe data acquisition/data processing device 104 to assist the subject108 with the execution of the proper limb and/or head rotation timing).The metronome provides an audible indicator of the pace at which thesubject's head and/or limbs should be rotated during the balance testand/or the concussion screening test. As such, the metronome supplementsthe inertial measurement unit (IMU) or the one or more visual indicators(i.e., light beam emitted from a light source that is rotated betweentwo markers disposed on a wall surface) described above. As such, whenthe metronome is used, the subject 108 is to rotate in sync with themetronome during the performance of the balance test and/or theconcussion screening test. The metronome may emit a predetermined numberof beats per minute (e.g., 30 beats per minute, 40 beats per minute, or50 beats per minute). The exact timing of the metronome will vary basedupon the particular subject or patient being tested.

In one or more further embodiments of the invention, a system formeasuring the postural sway, eye movement and/or eye position, and gazedirection utilizes a dual-task protocol to assess a medical condition ofa subject 108. The first task of the dual-task protocol may comprise aneurocognitive task (i.e. a task which requires a particular mentalprocess), while the second task of the dual-task protocol may comprise amotor or muscular task (i.e. a task which requires the use of muscles ofthe body). In one or more embodiments, the first cognitive task isperformed concurrently with the second motor task so that a subject hasto perform both tasks simultaneously.

An exemplary embodiment of a system for performing a dual task protocolis seen generally at 100′ in FIG. 8. The system of FIG. 8 is generallythe same as the system 100 described above, which is used for measuringthe postural sway, eye movement and/or eye position, and gaze directionof a subject 108. For example, like the system 100 described above, thesystem 100′ in FIG. 8 generally comprises a force measurement assembly102 that is operatively coupled to a data acquisition/data processingdevice 104 (i.e., a computing device that is capable of collecting,storing, and processing data), which in turn, is operatively coupled toan eye movement and eye position tracking device 124, and an operatorvisual display device 156. However, unlike the system 100 of FIG. 1, thesystem of FIG. 8 additionally includes a subject visual display device106, as well as the operator visual display device 156. Advantageously,providing two visual display devices 106, 156, allows both the subject108 and the clinician to have dedicated visual display devices (e.g.,content for the subject 108 may be displayed on the subject visualdisplay device 106, while the subject's performance is observed by theclinician on the operator visual display device 156).

With reference to FIGS. 8 and 9, the subject visual display device 106of the dual task assessment system 100′ will be described in moredetail. In the illustrated embodiment, like the operator visual displaydevice 156, the subject visual display device 106 is also in the form ofa flat panel monitor. Also, similar to the operator visual displaydevice 156, the subject visual display device 106 is operatively coupledto the data acquisition/data processing device 104 by means of a datatransmission cable 120. As described above for the operator visualdisplay device 156, those of ordinary skill in the art will readilyappreciate that various types of flat panel monitors having varioustypes of data transmission cables 120 may be used to operatively couplethe subject visual display device 106 to the data acquisition/dataprocessing device 104. For example, the flat panel monitor employed mayutilize a video graphics array (VGA) cable, a digital visual interface(DVI or DVI-D) cable, a high-definition multimedia interface (HDMI orMini-HDMI) cable, or a DisplayPort digital display interface cable toconnect to the data acquisition/data processing device 104.Alternatively, in other embodiments of the invention, the subject visualdisplay device 106 can be operatively coupled to the dataacquisition/data processing device 104 using wireless data transmissionmeans. As explained above for the operator visual display device 156,electrical power is supplied to the subject visual display device 106using a separate power cord that connects to a building wall receptacle.

Those of ordinary skill in the art will appreciate that the subjectvisual display device 106 can be embodied in various forms. For example,if the subject visual display device 106 is in the form of a flat screenmonitor as illustrated in FIG. 8, it may comprise a liquid crystaldisplay (i.e., an LCD display), a light-emitting diode display (i.e., anLED display), a plasma display, a projection-type display, or a rearprojection-type display. Although, it will be appreciated that thesubject visual display device 106 may take other forms as well, such asa head-mounted display, a heads-up display, or a 3-dimensional display.The subject visual display device 106 may also be in the form of a touchpad display.

In the dual task protocol, the first neurocognitive task may comprise avariety of different cognitive tasks. For example, the neurocognitivetask could require the subject to read one or more passages on a visualdisplay device, identify different colors, and identify differentletters, numbers, and/or symbols, or a pattern of different letters,numbers, and/or symbols displayed on the subject visual display device106. One of ordinary skill in the art will readily appreciate that theseare merely exemplary neurocognitive tasks, and that other suitableneurocognitive tasks may be employed in conjunction with the claimedinvention.

In the illustrative embodiment of FIGS. 8 and 9, the firstneurocognitive task requires the subject 108 to read a particularpassage 196 displayed on the subject visual display device 106. Whilethe subject is reading the passage 196 displayed on the subject visualdisplay device 106, the eye movement and eye position of the subject 108is tracked using the eye movement and eye position tracking device 124.

In the illustrative embodiment of FIGS. 8 and 9, as the subject 108reads the passage 196 on the visual display device 106, the eyemovements of the subject 108 are measured using the eye movement and eyeposition tracking device 124, while the head movements of the subject108 are measured using the head position detection device 122. In theillustrated embodiment, the data acquisition/data processing device 104may be specially programmed to compare the eye movements of the subject108 to the head movements of the subject 108 in order to determine ifthey are generally equal and opposite to one another. For a normalsubject, the head and eye movement tracings are approximately equal toone another in magnitude, but opposite in direction. If the head and eyemovements of the tested subject 108 are not approximately equal inmagnitude and opposite in direction, then the visual acuity of thesubject will deteriorate and the subject 108 will not be able to readthe passage 196 displayed on the subject visual display device 106. Thedata acquisition/data processing device 104 may be specially programmedto determine the amount of deviation between the subject's head and eyemovements, and to further determine if the subject 108 has lost visualacuity as a result of the deviation between the subject's head and eyemovements exceeding a predetermined deviation value. Also, during thetesting, the general reading ability of the subject 108 (i.e., theability to correctly read the passage 196 on the screen) may be assessedby the clinician or therapist. That is, during the testing, the subject108 reads the passage 196 on the subject visual display device 106, andthe clinician or therapist determines whether or not the subject 108read the passage 196 correctly or not (e.g., by assigning a readingscore to the subject 108). The data acquisition/data processing device104 may be specially programmed to receive and process this manualreading score for the subject 108, and to incorporate it into theoverall computed test score for the subject 108.

In an alternative embodiment, as the subject 108 reads the passage 196on the visual display device 106 (see FIGS. 8 and 9), the angular eyeposition of the subject 108 may be compared to the position of the textin the passage 196 on the screen of the visual display device 106 todetermine if the subject's reading pattern is normal. Initially, thedata acquisition/data processing device 104 may be specially programmedto determine a position of the text on the screen of the visual displaydevice 106. For example, the position of the text on the screen may bedefined in terms of pixel coordinates (x pixels by y pixels), which inturn, may be transformed into angular position coordinates (e.g., asshown in the screen image 162 of FIG. 14) so that the position of thetext may be compared to the angular eye position of the subject 108. Forexample, referring to FIG. 9, the starting center point of the firstline of the passage 196 in FIG. 9 may correspond to an angular positionof (−30°, 5°) while the ending center point of the first line of thepassage 196 in FIG. 9 may correspond to an angular position of (30°,5°). The starting center point of the second line of the passage 196 inFIG. 9 may correspond to an angular position of (−20°, −5°) while theending center point of the second line of the passage 196 in FIG. 9 maycorrespond to an angular position of (20°, 5°). As such, taking thefirst line of the passage 196 as an example, if the subject 108 isreading the text in a normal manner, his or her eyes should begin at anangular position generally corresponding to (−30°, 5°) and then the xcoordinate of the eye position should gradually increase from −30° to30° as the subject reads from left to right and reaches the end of thefirst line of text. While reading the first line of the passage 196, they coordinate of the eye position for the subject 108 should remaingenerally constant at an angular position of 5°. However, if the subject108 has a disorder, the x coordinate of the subject's eye position maynot consistently increase from −30° to 30° over time. Rather, if thesubject 108 is having difficulty reading the passage 196 in FIG. 9, thex coordinate of the subject's eye position may erratically increase anddecrease. In addition, if the subject 108 has a disorder that impairshis or reading ability, the y coordinate of the eye position for thesubject 108 may not remain generally constant at an angular position of5°, but rather may oscillate above and below the y coordinate positionof the first line of text (e.g., oscillate between 0° and 10°, etc.).

In another embodiment, the first neurocognitive task requires thesubject 108 to identify a letter, number, and/or symbol, or a pattern ofletters, numbers, and/or symbols displayed on the subject visual displaydevice 106. For example, the optotype “E” may be displayed on the screenof the subject visual display device 106, and the subject 108 may beasked to identify the direction of the optotype “E” on the screen (i.e.,identify whether the optotype “E” is pointing up, pointing down,pointing to the left, or pointing to the right). While the subject isidentifying the letters, numbers, and/or symbols, or a pattern ofletters, numbers, and/or symbols displayed on the subject visual displaydevice 106, the eye movement and eye position of the subject 108 istracked using the eye movement and eye position tracking device 124.

In yet another embodiment, the first neurocognitive task requires thesubject 108 to follow a moving target on the screen of the subjectvisual display device 106 while the eye movement and eye positiontracking device 124 is used to track the angular position of thesubject's eyes. In this embodiment, the data acquisition/data processingdevice 104 is specially programmed to assess the ability of the subject108 in tracking the moving target with his or her eyes. The performanceof the subject 108 during this test may be quantified using (i) an eyepursuit performance parameter specifying an amount that one or more eyesof the subject lag behind an intended target, (ii) an eye velocity ofone or more eyes of the subject, (iii) an eye pursuit performance ratioof eye velocity to target velocity for the subject, (iii) an accuracyparameter specifying an accuracy of one or more eyes of the subject, and(iv) an eye latency parameter specifying a time for the subject toinitiate eye movements.

In one or more embodiments, it is to be understood that variousperformance assessment parameters may be used to assess a subject'sperformance during the execution of the neurocognitive tasks set forthabove. For example, one or more of the following performance parametersmay be used to assess the subject's performance during the first task:(i) an eye pursuit performance parameter specifying an amount that oneor more eyes of the subject lag behind an intended target, (ii) an eyevelocity of one or more eyes of the subject, (iii) an eye pursuitperformance ratio of eye velocity to target velocity for the subject,(iii) an accuracy parameter specifying an accuracy of one or more eyesof the subject, and (iv) an eye latency parameter specifying a time forthe subject to initiate eye movements. In some embodiments, all of theaforementioned performance parameters (i), (ii), (iii), and (iv) may beused to assess the subject's performance during the first task.

Similarly, the second motor task may comprise a variety of differentmotor or muscular tasks, which are performed on the surface(s) of theforce measurement assembly 102 (e.g., the dual force plate in FIG. 8).For example, the motor or muscular task could require the subject tomaintain a substantially stationary, upright position on the forcemeasurement surface(s), or balance one or more objects while disposed onthe force measurement surface(s) (e.g., balancing a tray with empty cupsor cups filled with water disposed thereon). Similar to that which wasdescribed above for the cognitive tasks, one of ordinary skill in theart will readily appreciate that these are merely exemplary motor tasks,and that other suitable motor tasks may be employed in conjunction withthe claimed invention.

In addition, it is to be understood that various performance assessmentparameters may be used to assess a subject's performance during theexecution of the motor or muscular tasks set forth above. For example,one or more of the following performance parameters may be used toassess the subject's performance during the second task: (i) a maximumsway range of the center of pressure of a force vector applied by thesubject on the measurement assembly 102, (ii) a maximum sway range ofthe center of gravity of the subject 108, and (iii) a confidence areafor a path of the subject's center of pressure. In some embodiments, allof the aforementioned performance parameters (i), (ii), and (iii) may beused to assess the subject's performance during the second task.

As an alternative to, or in addition to the neurocognitive test, thesubject also may perform one of the other types of vestibular or ocularmotor tests described above in conjunction with the dual task protocol.In particular, as part of the dual task protocol, the subject may beinstructed to perform any one or more of the following other vestibularor ocular motor tests explained above: (i) a test involving smoothpursuits, (ii) a test involving saccades, (iii) a near point convergence(NPC) test, (iv) a vestibular-ocular reflex (VOR) test, and (v) a visualmotion sensitivity (VMS) test.

Initially, in the illustrative embodiment, at the beginning of thedual-task protocol, the subject 108 is positioned on the forcemeasurement assembly (102, 102′). If the dual force plate assembly 102is utilized for the dual-task protocol, the feet of the subject 108 willbe placed on respective first and second measurement surfaces 114, 116.In contrast, if the single force plate 102′ is used for the dual-taskprotocol, both feet of the subject will be placed on the singlemeasurement surface of the force plate 102′. Next, a scene is displayedon the subject visual display device 106 that relates to the performanceof the first neurocognitive task. For example, if the neurocognitivetask requires the subject 108 to read a particular passage, the subject108 is presented with one or more lines of text to read on the subjectvisual display device 106. Also, the subject 108 is instructed toperform the second motor task. As an example, the second motor ormuscular task may require the subject to maintain a substantiallystationary, upright position on the force measurement surfaces 114, 116of the force measurement assembly 102. Advantageously, during theexecution of the dual task protocol by the subject, the forcemeasurement assembly 102 is used to: (i) determine the subject'sperformance of the motor task and/or (ii) if the motor task requires acertain movement to be executed by the subject, verify that the motortask is actually being performed by the subject (i.e., to verify thatthe subject is not just focusing on the neurocognitive task and skippingthe motor task). In other words, during the dual task protocol, theforce measurement assembly 102 is used in an analytical manner. Whilethe subject performs the motor task, the force transducers of the forcemeasurement assembly 102 are used to sense the forces and/or momentsthat are applied to the surface of the force measurement assembly 102 bythe subject. The signals from the force transducers of the forcemeasurement assembly 102 are transmitted to the data acquisition/dataprocessing device 104, and the data acquisition/data processing device104 computes one or more numerical values (e.g., the subject's center ofpressure or center of gravity) from the signals.

In one or more embodiments, the force measurement assembly 102 is in theform of a static force plate (i.e., the force plate surface isstationary and is not displaced relative to the floor or ground). Such astatic force plate does not have any actuators or other devices thattranslate or rotate the force measurement surface. In one or morealternative embodiments, the force measurement assembly 102 is in theform of a dynamic force plate (i.e., the force plate surface isdisplaced and/or translated relative to the floor or ground). As such, adynamic force plate contains one or more actuators or other devices thatare capable of translating and/or rotating the force plate surface.

In the one or more embodiments, the data acquisition/data processingdevice 104 is specially programmed to compute the center of gravity(COG) for the subject 108 using the procedures described above (i.e.,approximation from the center of pressure (COP) using a Butterworthfilter, or direct computation of the center of gravity (COG)).

Then, the movements of the subject 108 are measured using the forcemeasurement assembly 102 in FIG. 8. The force measurement assembly 102outputs the one or more first signals that are generated based upon theone or more detectable movements on the surface 114, 116 of the forcemeasurement assembly 102. In addition, the eye movement and eye positionof the subject 108 is measured using the eye movement tracking device124, while one or more detectable movements of the subject 108 aresimultaneously measured by the force measurement assembly 102. The eyemovement tracking device 124 outputs one or more second signals that arerepresentative of the detected eye movement and eye position of thesubject 108 to the data acquisition/data processing device 104. Afterwhich, the data acquisition/data processing device 104 is speciallyprogrammed to compute one or more numerical values from the one or morefirst signals output by the force measurement assembly 102. The dataacquisition/data processing device 104 also is specially programmed todetermine one or more changes in eye position of the subject 108 fromthe one or more second signals output by the eye movement trackingdevice 124.

After the data acquisition/data processing device 104 computes the oneor more numerical values from the one or more first signals outputted bythe force measurement assembly 102 and determines the one or morechanges in eye position of the subject from the one or more secondsignals output by the eye movement tracking device 124, the dataacquisition/data processing device 104 may be specially programmed toquantitatively determine a subject's performance during the first andsecond tasks. The assessment of the subject's performance of the firsttask being based at least partially upon the one or more changes in eyeposition of the subject computed from the signals of the eye movementand eye position tracking device 124. The assessment of the subject'sperformance of the second motor task is based at least partially uponthe one or more numerical values computed from the signals of the forcemeasurement assembly 102. The subject's performance of the firstcognitive task is quantitatively expressed in terms of one or more firstperformance values, while the subject's performance of the second taskis quantitatively expressed in terms of one or more second performancevalues.

Finally, a medical condition of the subject 108 is assessed by using atleast one of the one or more first and second performance values (i.e.,one or more numerical scores). For example, in one or more embodiments,an inability to properly follow words in the passage 196 of FIGS. 8 and9 with one's eyes and a large sway range determined by the forcemeasurement assembly may be associated with a particular medicalcondition. In one or more embodiments, one or more changes in eyeposition of the subject's eye, as determined from the eye movement andeye position tracking device 124, and/or one or more numerical posturalsway values, as determined from the force measurement assembly 102,102′, may be used to predict if a subject 108 has a particular medicalcondition. In one or more embodiments, one or more of the followingmedical conditions may be assessed using at least one of the one or morefirst and second performance values: (i) a traumatic brain injury (TBI)or concussion, (ii) a neurological disorder or disease, and (iii) amuscular disorder or disease.

In one or more embodiments, the data acquisition/data processing device104 may further be specially programmed to combine the first performancevalue with the second performance value to obtain an overall combinedscore for assessing the medical condition of the subject 108. Forexample, a first performance value for the subject 108 may comprise ameasurement of how far behind the eyes lag a target (e.g., 10 degrees)that is moving on the screen of the subject visual display device 106.In an exemplary embodiment, a second performance value for the subject108 may comprise one of the following: (i) a maximum sway ofcenter-of-pressure (COP) (e.g., plus or minus 15 millimeters), (ii) amaximum sway of center-of-gravity (COG) about the ankle (e.g., plus orminus 7 degrees), and (iii) an area of ellipse fitted around the path ofthe COP with, for example, a 90 percent confidence area (e.g., 4.0 sq.centimeters). Considering the above examples, an overall combined scorefor assessing the medical condition of the subject 108 may comprise oneof the following: (i) a first performance value of 10 degrees multipliedby a second performance value of 15 millimeters so as to obtain anoverall combined score of 150 (i.e., 10×15), (ii) a first performancevalue of 10 degrees multiplied by a second performance value of 7degrees so as to obtain an overall combined score of 70 (i.e., 10×7),and (iii) a first performance value of 10 degrees multiplied by a secondperformance value of 4.0 sq. centimeters so as to obtain an overallcombined score of 40 (i.e., 10×4.0), depending on which of the abovebalance scoring techniques is utilized. The final score result(s) may becompared with the score for a normal subject. When one or more of theindividual scores or their product (as illustrated above) is not normal,this may be indicative of a particular medical condition.

In addition, the data acquisition/data processing device 104 may bespecially programmed to determine whether or not a subject 108 has aparticular medical condition (e.g., a traumatic brain injury (TBI) orconcussion) by testing the subject 108 before and after a particularevent has occurred. For example, on day 1, prior to engaging in anyathletic activities involving substantial contact with other players oranother object (e.g., football or ice hockey), a first subject 108 istested several times using the system 100′ of FIG. 8, and has a meanfirst performance value of 5 degrees (i.e., an angular measurement ofhow far behind the eyes lag the target) for the neurocognitive taskafter being tested for three trials thereof, and a mean secondperformance value of plus or minus 3 degrees (i.e., a maximum sway ofcenter-of-gravity (COG) about the ankle) for the motor or muscular taskafter being tested for three trials thereof, resulting in an overallcombined score of 15 (i.e., 5×3). Subsequently, on day 30, after playingfootball, and sustaining a severe impact to the head during a tackle,the same first subject is again tested on the system 100′ of FIG. 8.However, on day 30, the first subject has an increased mean firstperformance value of 15 degrees for the neurocognitive task after beingtested for three trials thereof, and an increased mean secondperformance value of plus or minus 10 degrees for the motor or musculartask after being tested for three trials thereof, resulting in anoverall combined score of 150 (i.e., 15×10). Based upon a comparison ofthe initial average combined score of 15 to the subsequent averagecombined score of 150, the data acquisition/data processing device 104of the system 100′ of FIG. 8 determines that the first subject has“Possibly Sustained a Concussion”.

As another example, on day 1, prior to engaging in any athleticactivities involving substantial contact with other players or anotherobject (e.g., football or ice hockey), a second subject 108 is testedseveral times using the system 100′ of FIG. 8, and has a mean firstperformance value of 8 degrees (i.e., an angular measurement of how farbehind the eyes lag the target) for the neurocognitive task after beingtested for three trials thereof, and a mean second performance value ofplus or minus 6 degrees (i.e., a maximum sway of center-of-gravity (COG)about the ankle) for the motor or muscular task after being tested forthree trials thereof, resulting in an overall combined score of 48(i.e., 8×6). Subsequently, on day 45, after playing ice hockey, andsustaining a blow to the head from an opponent's hockey stick, the samesubject is again tested on the system 100′ of FIG. 8. However, on day45, the second subject has only a slightly increased mean firstperformance value of 9 degrees for the neurocognitive task after beingtested for three trials thereof, and a slightly decreased mean secondperformance value of plus or minus 5 degrees for the motor or musculartask after being tested for three trials thereof, resulting in anoverall combined score of 45 (i.e., 9×5). Based upon a comparison of theinitial average combined score of 48 to the subsequent average combinedscore of 45, the data acquisition/data processing device 104 of thesystem 100′ of FIG. 8 determines that the subject “Does Not ReadilyAppear to Have Sustained a Concussion”. In some instances, the dataacquisition/data processing device 104 may also conclude that it is“Indeterminable Whether or Not Subject Has Sustained a Concussion”(e.g., when scores achieved by the subject are too erratic). At theconclusion of the testing, the predicted medical condition evaluation ofthe subject is outputted to the subject visual display device 106 and/orthe operator visual display device 156 so that the subject and/or theclinician can be informed of whether or not the subject appears to havea particular medical condition.

In one or more embodiments of the invention, a series of tests areperformed in conjunction with the dual-task protocol. For example, inone such variation, the subject initially will be asked to perform aneurocognitive task (e.g., reading a particular passage that isdisplayed on the subject visual display device 106). Next, the subjectwill be instructed to perform a motor/muscular task (e.g., balancing atray with empty cups or cups filled with water disposed thereon).Finally, the subject will be asked to perform both the cognitive taskand the motor/muscular task simultaneously (i.e., the performance ofdual tasks). Moreover, the results during each of the tests can also becompared to the results from a baseline test (i.e., results generatedduring tests that were performed before the subject 108 had experiencedthe medical condition being assessed, when the subject was consideredhealthy).

In addition, in an alternative embodiment, a pressure measurementassembly or a contact/timing measurement assembly (e.g., a contact matwith time measurement capabilities) may be used in lieu of the forcemeasurement assemblies 102, 102′. For example, in these alternativeembodiments, the force transducers 160 disposed underneath the topplates may be replaced with pressure transducers in the case of apressure measurement assembly, and may be replaced with contact ortiming switches in the case of a contact/timing measurement assembly.Pressure measurement assemblies could be used to output the subject'sfoot pressure distribution and/or force and pressure time integralscomputed using the subject's foot pressure distribution. Contact/timingmeasurement assemblies (e.g., contact mats), if substituted for each ofthe force measurement assemblies 102, 102′, could be used to output thetime duration between the subject's successive contact periods with themat surface. As such, the rhythm and timing of the subject could bedetermined during the performance of the motor task so that it could bedetermined whether or not the motor task was being properly performed bythe subject.

In one or more embodiments of the invention, the system 100′ of FIG. 8is used to determine a subject's point of failure during the dual taskprotocol and/or determine the task during which the subject's failureoccurs (e.g., a failure occurs during the neurocognitive task or themotor task). For example, during the performance of the second motortask, it may be determined that the failure occurs when the subjectleans too much while performing the motor task. The subject's inabilityto perform the motor task without falling may be indicative of musculardisorder. Alternatively, the failure may occur during the performance ofthe neurocognitive task, which may be indicative of a cognitivedisorder. Advantageously, once the subject's deficiency or deficienciesare identified, the appropriate corrective measures can be taken (e.g.,if the failure occurred during the motor task, measures can be taken totreat the muscular disorder).

It is readily apparent that the embodiments of the system 100, 100′ formeasuring eye movement and/or eye position and postural sway of asubject described above offer numerous advantages and benefits. Thesesame advantages and benefits are realized by the methods that utilizethe system 100, 100′. In particular, the systems and methods discussedherein, which measure eye movement and/or eye position and postural swayof a subject, enable head, eye, and postural movements to bequantitatively evaluated during head-eye coordination exercises.Moreover, the systems and methods described herein enable a patient'sfunctional status to be objectively documented before, during, aftertherapy. Furthermore, the systems and methods discussed herein, whichmeasure eye movement and/or eye position and postural sway of a subject,enable a medical condition to be assessed (e.g., a traumatic braininjury (TBI) or concussion) so that the proper treatment procedures canbe implemented. As such, it is readily apparent from the variousadvantages and benefits described herein that the system 100, 100′ formeasuring eye movement and/or eye position and postural sway of asubject, and the methods practiced using the system 100, 100′,significantly advance the interrelated fields of vision, vestibular, andbalance assessment.

Moreover, while reference is made throughout this disclosure to, forexample, “one embodiment” or a “further embodiment”, it is to beunderstood that some or all aspects of these various embodiments may becombined with one another as part of an overall embodiment of theinvention. That is, any of the features or attributes of theaforedescribed embodiments may be used in combination with any of theother features and attributes of the aforedescribed embodiments asdesired.

Although the invention has been shown and described with respect to acertain embodiment or embodiments, it is apparent that this inventioncan be embodied in many different forms and that many othermodifications and variations are possible without departing from thespirit and scope of this invention.

Moreover, while exemplary embodiments have been described herein, one ofordinary skill in the art will readily appreciate that the exemplaryembodiments set forth above are merely illustrative in nature and shouldnot be construed as to limit the claims in any manner. Rather, the scopeof the invention is defined only by the appended claims and theirequivalents, and not, by the preceding description.

The invention claimed is:
 1. A method for concurrently measuring thehead position and postural sway of a subject, the method comprising thesteps of: providing a head position measurement device configured tomeasure a position of a head of the subject while the subject performs abalance test and/or a concussion screening test, the head positionmeasurement device comprising a light source configured to project alight beam onto a surface in front of the subject and a plurality ofspaced-apart markers disposed on the surface so that a path of the lightbeam is able to be compared to the plurality of spaced-apart markers, afirst one of the plurality of spaced-apart markers corresponding to afirst intended angular position of the head of the subject, and a secondone of the plurality of spaced-apart markers corresponding to a secondintended angular position of the head of the subject, the first one ofthe plurality of spaced-apart markers being spaced apart from the secondone of the plurality of spaced-apart markers by a predetermined headdisplacement angular range; providing a postural sway detection device,the postural sway detection device configured to detect a postural swayof the subject while the subject performs the balance test and/or theconcussion screening test, the postural sway detection device beingconfigured to output one or more signals that are representative of thedetected postural sway of the subject; providing a visual target that isa portion of one or more limbs of the subject; providing a dataprocessing device operatively coupled to the postural sway detectiondevice, the data processing device configured to receive the one or moresignals that are representative of the detected postural sway of thesubject, the data processing device further configured to determine thepostural sway of the subject using the one or more signals; positioningthe subject in an upright position on a surface; instructing the subjectto displace his or her head back and forth in an oscillatory manner overa prescribed angular range; instructing the subject to displace his orher head and the one or more limbs back and forth in an oscillatorymanner over the prescribed angular range while the subject maintains hisor her gaze on the visual target; measuring the position of the head ofthe subject using the head position measurement device by projecting thelight beam from the light source onto the surface, and then comparingthe light beam to the first one of the plurality of spaced-apart markersand the second one of the plurality of spaced-apart markers on thesurface; measuring the postural sway of the subject using the posturalsway detection device while measuring the position of the head of thesubject, and outputting the one or more signals that are representativeof the postural sway of the subject from the postural sway detectiondevice; determining, by using the head position measurement device, anangular position of the head of the subject as the subject displaces hisor her head over the prescribed angular range; determining, by using thedata processing device, postural sway data for the subject from the oneor more signals output by the postural sway detection device; anddetermining whether the subject is displacing his or her head over theprescribed angular range by comparing the angular position of the headof the subject determined by using the head position measurement deviceto the predetermined head displacement angular range.
 2. The methodaccording to claim 1, wherein the postural sway detection devicecomprises at least one of the following: (i) a force or balance plate,(ii) one or more inertial measurement units, (iii) an optical motioncapture device, (iv) an infrared motion capture device, and (v) amarkerless motion capture device; and wherein the step of measuring thepostural sway of the subject using the postural sway detection devicefurther comprises measuring the postural sway of the subject using atleast one of: (i) the force or balance plate, (ii) the one or moreinertial measurement units, (iii) the optical motion capture device,(iv) the infrared motion capture device, and (v) the markerless motioncapture device.
 3. The method according to claim 1, wherein the posturalsway detection device comprises a force or balance plate, the force orbalance plate including: a force receiving component having a topsurface for receiving at least one portion of the body of the subject;and at least one force transducer disposed underneath the forcereceiving component, and the at least one force transducer supportingthe force receiving component, the at least one force transducerconfigured to sense one or more measured quantities and output the oneor more signals, the one or more signals being representative of forcesand/or moments being applied to the top surface of the force receivingcomponent of the force measurement assembly by the subject, and the atleast one force transducer comprising a pylon-type force transducer or aforce transducer beam.
 4. A method for concurrently measuring the headposition and postural sway of a subject, the method comprising the stepsof: providing a head position measurement device configured to measure aposition of a head of the subject while the subject performs a balancetest and/or a concussion screening test, the head position measurementdevice comprising at least one of the following: (i) a video camera,(ii) an infrared sensor, (iii) an ultrasonic sensor, (iv) a light sourceconfigured to project a light beam onto a surface, and (v) a markerlessmotion capture device; providing a postural sway detection device, thepostural sway detection device configured to detect a postural sway ofthe subject while the subject performs the balance test and/or theconcussion screening test, the postural sway detection device beingconfigured to output one or more signals that are representative of thedetected postural sway of the subject; providing a data processingdevice operatively coupled to the postural sway detection device, thedata processing device configured to receive the one or more signalsthat are representative of the detected postural sway of the subject,the data processing device further configured to determine the posturalsway of the subject using the one or more signals; positioning thesubject in an upright position on a surface; providing a visual targetthat is a portion of one or more limbs of the subject; instructing thesubject to displace his or her head and the one or more limbs back andforth in an oscillatory manner over a prescribed angular range while thesubject maintains his or her gaze on the visual target; measuring theposition of the head of the subject using the head position measurementdevice that comprises at least one of: (i) the video camera, (ii) theinfrared sensor, (iii) the ultrasonic sensor, (iv) the light sourceprojecting the light beam onto the surface, and (v) the markerlessmotion capture device; measuring the postural sway of the subject usingthe postural sway detection device while measuring the position of thehead of the subject, and outputting the one or more signals that arerepresentative of the postural sway of the subject from the posturalsway detection device; determining, by using the head positionmeasurement device, an angular position of the head of the subject asthe subject displaces his or her head over the prescribed angular range;determining, by using the data processing device, postural sway data forthe subject from the one or more signals output by the postural swaydetection device; and determining whether the subject is displacing hisor her head over the prescribed angular range by comparing the angularposition of the head of the subject determined by using the headposition measurement device to a predetermined head displacement angularrange.
 5. The method according to claim 4, wherein the head positionmeasurement device comprises a light source configured to project alight beam onto a surface and a plurality of spaced-apart markersdisposed on the surface so that a path of the light beam is able to becompared to the plurality of spaced-apart markers, a first one of theplurality of spaced-apart markers corresponding to a first intendedangular position of the head of the subject, and a second one of theplurality of spaced-apart markers corresponding to a second intendedangular position of the head of the subject, the first one of theplurality of spaced-apart markers being spaced apart from the second oneof the plurality of spaced-apart markers by the predetermined headdisplacement angular range.
 6. The method according to claim 4, whereinthe postural sway detection device comprises at least one of thefollowing: (i) a force or balance plate, (ii) one or more inertialmeasurement units, (iii) an optical motion capture device, (iv) aninfrared motion capture device, and (v) a markerless motion capturedevice; and wherein the step of measuring the postural sway of thesubject using the postural sway detection device further comprisesmeasuring the postural sway of the subject using at least one of: (i)the force or balance plate, (ii) the one or more inertial measurementunits, (iii) the optical motion capture device, (iv) the infrared motioncapture device, and (v) the markerless motion capture device.
 7. Themethod according to claim 4, wherein the postural sway detection devicecomprises a force or balance plate, the force or balance plateincluding: a force receiving component having a top surface forreceiving at least one portion of the body of the subject; and at leastone force transducer disposed underneath the force receiving component,and the at least one force transducer supporting the force receivingcomponent, the at least one force transducer configured to sense one ormore measured quantities and output the one or more signals, the one ormore signals being representative of forces and/or moments being appliedto the top surface of the force receiving component of the forcemeasurement assembly by the subject, and the at least one forcetransducer comprising a pylon-type force transducer or a forcetransducer beam.